Koichi Hirose

"In case you're wondering, my name is Koichi Hirose (though I guess it's not that important). Anyway, I was nervously walking myself to class... until I met those two really strange guys."

- Koichi Hirose

Koichi Hirose (広瀬 康一) is a deuteragonist of Diamond is Unbreakable and appears briefly as a minor character in Vento Aureo.

Koichi is a timid high-school first-year who befriends Josuke Higashikata and then finds himself entangled in the world of Stand users.

Koichi also becomes a Stand User and wields Echoes.

Appearance
Koichi is a teenage boy of below average height, 157 cm (5'2") tall and average build, though he's typically depicted shorter. He wears a notably unmodified student uniform, otherwise preferring leisure wear.

Koichi first keeps his light hair neatly combed back. During his confrontation with Tamami, it gains the tendency to rise into spikes when he is excited (producing a look similar to that of Dragon Ball Z character Gohan at Super Saiyan 2 during the Cell Games). Towards the end of his confrontation with Yukako, he suddenly cuts his hair, producing a flat-top, which spontaneously grows out again into spikes during his battle with Yoshikage Kira. The color of his hair varies throughout the media, the most common schemes being blond, blue, or silver.

Heaven's Door reveals that Koichi was born prematurely weighing only 2325 grams (5 lbs 2 oz), and was kept in intensive care for 7 days.

In Vento Aureo, Koichi's jacket is replaced with a much longer double-breasted variation featuring metallic wristbands and the roman numeral for three (III) on each side of his collar.

Personality
Koichi is an amiable, but meek youth who undergoes an exceptional degree of character development over the course of Diamond is Unbreakable, becoming more assertive throughout many confrontations with evil Stand users. His greatest leaps are illustrated by the metamorphosis of his Stand, Echoes.

One of Koichi's constant traits is his friendliness and overall politeness toward any stranger and acquaintance. Having a gentle heart, Koichi usually doesn't seek to harm his opponents, notably having saved Yukako from death even though she wanted to kill him before, and briefly fighting Giorno Giovanna without using the strength to kill, which inadvertently saved him. However, Koichi's friendliness disappears on the rare occasions he is angered, and he becomes more abrasive, violent and vulgar.

Koichi also possesses a rather cheerful personality. He finds wonder in most things (such as his new bike, a famous mangaka living in town, finding an error in a map, etc.), and has little trouble befriending people. Because of this, he is usually easily pressured into an interlocutor's demands, such as Tamami Kobayashi effortlessly extorting him, or Rohan pushing him into spending time with him. Much like any ordinary teenager, Koichi is interested in more accessible distractions. He is a great fan of Rohan Kishibe's manga Pink Dark Boy and plans to visit but expresses no interest in "old" countries such as Italy.

Another one of Koichi's primary characteristics is his courage and associated virtuousness. As revealed by Heaven's Door, Koichi is described as cowardly, but courageous when push comes to shove. True to that assertion, Koichi is very prone to express anxiety, fear, and despair at various setbacks, such as his battles against Yukako, Rohan or Sheer Heart Attack. Terunosuke states that when Koichi is scared he blinks twice. In addition, Koichi mentions during the Atom Heart Father arc that he has claustrophobia. Still, Koichi soldiers on and braves danger despite his fears. Initially weak-willed, acquiring a Stand and fighting others made him more confident in himself and assertive, going from being bullied by upperclassmen to facing down and taunting Yoshikage Kira while on the verge of death. By Vento Aureo, Koichi has grown into a confident youth who, while still prone to bouts of panic, could enter a Stand fight without qualms.

The mix of his gentleness and courage make Koichi an extremely likable individual, earning the friendship and respect of the vast majority of the cast including Josuke Higashikata, Tamami Kobayashi, Toshikazu Hazamada, Rohan Kishibe, Yukako Yamagishi, Aya Tsuji, and Jotaro Kujo.

Koichi is a relatively perceptive individual, able to make quick and decisive moves in a fight, sometimes at the cost of being too imprudent. For the most part, Koichi tries to analyze his situation before acting, notably due to how weak his Stand is at the start of the series and the severe limitations of his powers, but sometimes misses a critical consequence of his actions.

After a difficult start in his relationship with Yukako, due to her kidnapping Koichi, he eventually fell in love with Yukako's tough and unforgiving personality. His love was such that he was willing to be blinded forever in case Yukako became ugly, so as to ease her pain.

Abilities
Koichi's Stand, Echoes, starts off with ACT1 only. As Part Four progressed, Echoes evolves, giving Koichi new abilities to use. By the end of Part Four, Echoes gains ACT2 and ACT3. He is able to willingly call upon Echoes' previous ACT forms at will and utilize their unique abilities.

ACT1 enables him to write on any surface, causing the words or onomatopoeia to continuously repeat at various volumes.

ACT2 enables him to write a sound effect on any surface. If the word is touched, a special effect related to the sound effect is activated.

ACT3, a humanoid Stand, facilitates conventional melee attack and the ability to "freeze" targets by ascribing them unbearable weight.

Mastery
Thanks to Echoes' three forms, Koichi is presented with a wide array of options. For direct combat, Koichi favors using his latest ACT, almost exclusively using Echoes ACT3 when he unlocks it despite ACT2's potential for versatility. With Echoes ACT3, Koichi makes ample use of his weighting power to immobilize enemies but its restricted effects do not lend themselves to the imagination.

Koichi also regularly uses ACT1 as a scout, using its great range of 50 meters to watch his surroundings.

Background
Up until the events of the manga, Koichi has lived an ordinary life as a Japanese boy. It is known that he was born at the Red Cross Hospital in S City on March 28, 1984 at 6:27 AM. He was born prematurely, only weighting 2325g and kept in intensive care for 7 days.

Koichi meets the Joestars
Koichi is a first-year student in class 1-B of Budogaoka Highschool. On the first day of school, he meets Jotaro Kujo and Josuke Higashikata, learning that they have extraordinary powers. Josuke being his first acquaintance in highschool, Koichi and him quickly become friends.

Some time later, Koichi is shot with the Bow and Arrow by Keicho Nijimura, who was searching for a Stand capable of killing his father. Koichi develops the egg-shaped Stand Echoes, whose ability is still unknown, and bears witness to Josuke's battle against Keicho as well as the theft of the Arrow by Red Hot Chili Pepper.

Fighting malevolent Stand Users
Koichi remains well-involved with the overall plot, his Stand even evolving multiple times as he fights a few battles on his own. He is a victim of the con artist Tamami Kobayashi, who threatens his family in exchange for money. In this battle, Koichi develops Echoes ACT1 and defeats Tamami, who later befriends him.

With the help of Tamami, Koichi investigates the Stand user Toshikazu Hazamada and tries to fight him alongside Josuke. Hazamada is ultimately defeated.

Yukako Yamagishi Falls in Love
Yukako, a fellow student in love with him, at first proved to be very difficult for him to deal with as she was very aggressive in her affections towards him. Koichi tried to look like a "bad guy" to keep her away but this plan backfires as she goes to the point of kidnapping him and threatening his life should he not appreciate her efforts to "change him into a better person". Koichi defeats her in battle after developing Echoes ACT 2 but saves her life in the end.

Red Hot Chili Pepper
Akira Otoishi reveals later that Koichi was one of the Stand users he watched with his Red Hot Chili Pepper. Koichi then participates little in the battle against Akira, his weak long-ranged Echoes being used as a liaison between him on the port and Jotaro on the boat.

Koichi & Rohan Kishibe
Some time later, Koichi somewhat befriends Hazamada over their shared love of mangas. The pair goes to the house of famous mangaka Rohan Kishibe to ask for an autograph and are even invited inside. Rohan baits the students into looking at his art and they get turned into books by Rohan's Heaven's Door as a result. Rohan takes a keen interest in Koichi for his admirable personality and decides to brainwash him to serve as a muse. Thankfully, Josuke and Okuyasu intervene to beat Rohan and rein in his obsession.

A month later, Rohan and Koichi meet again. The two accidentally discover the Ghost Girl's Alley and explore it only to find Reimi Sugimoto, who explains that a killer has been lurking in town for decades. On the way out, Koichi is almost abducted by the malicious spirits of the alley but Rohan saves him. Koichi goes on to warn Josuke and Okuyasu about the killer.

Yukako Yamagishi Dreams of Cinderella
When Yukako searches for Aya Tsuji's help, Koichi is beginning to be attracted to Yukako. He even offers to become blind in case he fails to help Yukako return to her old appearance (changed by Cinderella). Later in the story, still lovestruck, she seemed to have learned from her mistakes in trying to force him and approached him more carefully, upon which Koichi warmed up to her and slowly, willingly, became her boyfriend.

Investigating Yoshikage Kira
After Shigechi is killed by the murderer Yoshikage Kira, Koichi becomes deeply involved with the investigation. He and Jotaro Kujo almost discover Kira's identity but must fight off Killer Queen's Sheer Heart Attack ability. During that battle, Jotaro is grievously wounded but Koichi actually develops Echoes ACT3 and stops Sheer Heart Attack. Kira comes soon after and defeats Koichi, who nonetheless remains defiant until Killer Queen impales him on his fist. Koichi almost dies but is saved by Jotaro and healed by Josuke. The group fails to capture Kira, who takes a new identity because of Aya Tsuji's Cinderella.

Later, Koichi, along with Josuke, Okuyasu and Jotaro search Kira's house, but the group is attacked by Kira's father, Yoshihiro. Yoshihiro is captured but tricks Okuyasu into releasing him and he flees with another Arrow.

Cornering Yoshikage Kira
Since Yoshikage has a new identity, Rohan and Jotaro take it upon themselves to investigate all the commuters in town, letting Yoshihiro Kira the chance to make several Stand Users and sic them at the heroes.

During Josuke's encounter with Highway Star, Koichi helps locate Yuya Fungami by tracking his Stand.

Koichi is kidnapped by Terunosuke Miyamoto, who traps him in a piece a paper with his Stand, Enigma. His life is put into danger when Terunosuke throws Koichi in front of a car, but he ends up being saved by Yuya.

Koichi also tries to save Rohan from Cheap Trick but almost rips out Rohan's back in the process.

Crazy Diamond is Unbreakable
Koichi finally finds Yoshikage Kira again and is fundamental to his defeat, as he multiplies the weight of Kira's left hand before he can activate his Bites the Dust ability. As Kira is accidentally killed by an ambulance, Koichi looks away in horror. After Kira's death, he then sees off Reimi as she, along with her dog, goes to heaven.

(The information below derives from the TV Anime. As such, it may or may not be considered .)

He is seen hanging out with Yukako next to the Angelo rock and wants to eat a lunch she made and holds her hand as they walk. He is later seen talking to Josuke and Okuyasu about a rumor the latter heard about Rohan being caught shoplifting at Kame Yu.

The Book: 4th Another Day
The information below derives from a Light Novel not written by Araki. As such, it may or may not be considered.

After the events of Part 4, Koichi and Rohan find a cat (named Trinita) covered in blood and the two try to find his master. Koichi soon discovers that Hanae Orikasa, the cat's master, was killed under mysterious circumstances and tags along with Rohan to find the killer. After taking Trinita from the police station via Echoes, they discover, with the help of Heaven's Door, that the killer might be a Stand user, and has a very distinct characteristic: red marks on his arms.

Koichi later works with Yukako to discover if the killer is from the same class as them, using his Echoes ACT2. Learning the fact that there are multiple students in the school with this feature, Koichi tries figuring out the secret inside this. After Koichi knows about Josuke's mother Tomoko getting attacked, he meets up one of his schoolmates with red marks on his arms, asks him about this, and gets surprised with his response that he actually did this by himself. Then Rohan comes and uses Heaven's Door to read the schoolmate's memory. By reading his memory, Rohan deducts the Stand ability of the culprit and erases those made-up memories. After this investigation, Koichi asks Rohan to erase the memories from Tomoko as well.

Later, in March 2000, with Rohan's investigation, Koichi and his fellows have more information about Hanae Orikasa and the culprit. When Koichi and Yukako are studying at Thorn Parlour (Morioh public library), they encounter Chiho Futaba. Koichi is a little confused to know that Chiho knows his name.

On a snowy day, Koichi goes home by bus after school and runs into Josuke. They talk a little about the pompadour young man who saved Josuke's life when he was 4. Then Koichi glances a slide. They run to the spot and find an orphanage. After they ask the staff and the dean, Josuke and Koichi are quite sure that Takuma Hasumi is the culprit they are chasing. After getting Takuma's address, Koichi and Josuke decide to go to his home the next day.

That night, Koichi is informed by Yukako that Chiho's home is on fire, so he immediately calls Josuke, who doesn't reply and is actually on his way to Takuma's home. Josuke calls back when he fails to find Takuma in his home, then Koichi tells Josuke that Takuma might be at Thorn Palace now. Finishing the phone call, Koichi starts walking to Thorn Palour. Koichi also calls Okuyasu and tells him to go to Thorn Parlour on his way. It's assumed that the battle between Josuke and Takuma is already over when Koichi eventually arrives Thorn Palour, and Koichi calls the ambulance and police anonymously.

In August 2000, Koichi comes across Chiho accidentally, who is now living with her mom outside Morioh. After some chatting, he is astonished to find out Chiho is pregnant with Takuma, her half brother's child. Deciding to keep this encounter as a secret, Koichi prays that Chiho and her child will have a good future when Chiho is leaving Morioh.

Rohan at the Louvre
Koichi makes a brief appearance, hearing Rohan's story about Nanase Kishibe along with Okuyasu and Josuke. Koichi questions Okuyasu about his opinion on Rohan's likeness with Mona Lisa, as they have different genders.

Gold Experience
Jotaro sends Koichi to Naples, Italy to locate Haruno Shiobana in order to get a skin sample for the Speedwagon Foundation to test, having asked Rohan to write 'Italian language skills' into him with Heaven's Door to make the ordeal easier. Shortly after arriving, Koichi notices Giorno performing in the street and then subtly bribing the policemen watching. Giorno offers to give him a ride, but Koichi refuses until noticing the long line of people waiting for a taxi. Unfortunately, the offer was a trick and Giorno starts to drive off with Koichi's luggage before he can get in the car. Using Echoes ACT3, Koichi stops the car but Giorno simply smiles and flees the scene after transforming the luggage it into a frog. Koichi overhears the nearby policemen talking about Giorno's failure and realizes that "Giorno Giovanna" is actually the "Haruno Shiobana" he'd been sent to find. He doesn't, however, figure out that the frog he found in the back of the car is actually his luggage.

Gang Enrollment
Sometime later, when Giorno is undergoing the test to join Passione, Koichi locates his apartment and searches for his missing luggage. He nearly extinguishes the lighter flame which Giorno had stood in a loaf of bread, but Giorno whisks it away with Gold Experience just in time. Having successfully found his passport, Koichi leaves the apartment building only to stumble upon Giorno and a dead janitor. At first, he believes Giorno is responsible but soon learns that it was Black Sabbath's doing. He ends up helping Giorno to defeat the Stand, noticing in the process that it possesses part of the Bow and Arrow. Koichi then accesses a payphone to inform Jotaro, but Giorno stops him and Koichi decides to remain quiet in deference to Giorno's virtuousness and behavioral similarity to those of the Joestar bloodline in the manga. In the anime, Giorno trusts him enough to tell him everything. Koichi continues his trip and he gives the report to Jotaro when he gets home. It's implied Koichi stood up for him since Jotaro doesn't pursue Giorno anymore.

Allies

 * Josuke Higashikata: One of Koichi's main best friends, the two quickly got along the first moment they met. Koichi admires Josuke and looks up to him while considering him a kind strong person. In turn, Josuke also relies on Koichi during battles and is impressed by his bravery. Josuke is willing to help him whenever he can, such as when Yukako goes after Koichi.
 * Okuyasu Nijimura: The two met on bad terms as Okuyasu slammed some doors between Koichi's neck nearly choking him. However, they moved on from that and became friends. While Koichi and Okuyasu do not have much interaction, they've shown to care for each other's well-being. Okuyasu was concerned when Koichi was kidnapped by Yukako and during the Red Hot Chili Pepper arc, Koichi was sympathetic and comforting to Okuyasu's plight and desire for vengeance against Red Hot Chili Pepper. Nonetheless, Okuyasu is mildly jealous of Koichi's relationship with Yukako, as Okuyasu himself hasn't had a girlfriend.
 * Jotaro Kujo: Koichi looks up to Jotaro as a strong ally, although he is put off by Jotaro's aloof temperament. Their cooperation during the Sheer Heart Attack story arc had Jotaro act as a mentor figure to Koichi, who came to really respect Jotaro's prowess in battle. In addition, Jotaro also grows to see Koichi as a good friend and a reliable person, enough so that he chose him to go to Italy and investigate Giorno Giovanna.
 * Rohan Kishibe: Koichi first admired Rohan as a talented mangaka, but his view changed quickly upon their first meeting when he and Toshikazu Hazamada went to visit Rohan. While Rohan liked Koichi and grew to see Koichi as his first (and possibly only) true friend, he was still abrasive and pushy, notably pressuring him to accompany him on two occasions, and Koichi tolerated less and less the worst sides of Rohan's arrogance as he gained confidence and he was overall a positive influence on Rohan's attitude. At the end of Diamond is Unbreakable, one reproachful look from Koichi was enough for Rohan to yield and confess an attachment to Reimi Sugimoto.
 * Yukako Yamagishi: When Yukako first confessed her feelings to him, Koichi was happy but quickly lost interest upon learning of her obsessive personality, made worse when she kidnapped him. He managed to defeat her and remained somewhat frightened of her. However, during the Cinderella arc, Koichi sought to reconcile with her and grew attracted to her forceful and aggressive personality, ultimately the two became a couple. Koichi's affection for Yukako was such that he was willing to blind himself if Yukako ended up being ugly due to Cinderella's power in order to ease her pain.
 * Reimi Sugimoto: The two met when he and Rohan stumbled upon the haunted alleyway she resided in. While initially scared upon hearing she was a ghost, he quickly sympathized with her after hearing her tragic story and promised to find her killer so she may rest in peace. He later bids her farewell when she ascends to heaven and was rather saddened with her parting. He also gave Rohan a reproachful look so he would admit he would miss Reimi too.
 * Tamami Kobayashi: Initially Tamami tried to scam Koichi with his stand, but Josuke and Okuyasu intervened. When Tamami tried to involve Koichi's family, Koichi got so angered he awakened his Stand and beat Tamami. Since then, Tamami has become afraid of Koichi but also genuinely respects him. Their relationship has been described as a one-sided boss-subordinate relationship.
 * Toshikazu Hazamada: Koichi and Josuke fought him and quickly defeated him. Afterward, Hazamada somewhat bonded with Koichi over their mutual interest in Pink Dark Boy and the two went to visit Rohan's place. Their relationship has been described as a one-sided friendship.
 * Aya Tsuji: While the two had little interaction, Aya grew to respect Koichi's determination when she saw his willingness to blind himself if he couldn't help Yukako through the trial Aya put her through. He was also saddened when Kira killed her.
 * Family: While not much interaction was shown with his family (which consists of his parents and older sister), when Tamami tried to use them to get revenge on Koichi, he became enraged enough to beat Tamami by awakening his Echoes ACT1 Stand, demonstrating that he cared for them. His relationship with his father is never shown but is presumed to be good.
 * Giorno Giovanna: Koichi was sent to investigate Giorno by Jotaro, and Giorno did his best to avoid Koichi even turning his suitcase into a frog. However, over time Koichi grew to see Giorno's noble soul. He reports to Jotaro after the trip, but he convinces Jotaro that Giorno is a good person.

The Book: JoJo's Bizarre Adventure 4th Another Day

 * Chiho Futaba: Koichi firstly meets Chiho in Thorn Palour while studying with Yukako, and gets to know her through Yukako's introduction. He runs into Chiho again about 5 months after Takuma Hasumi's case. Surprised to find out that Chiho is pregnant with Takuma's baby, Koichi decides to keep this encounter as a secret and sees Chiho leaving Morioh, sending his wishes to her.
 * Takuma Hasumi: After discovering Trinita and Hanae Orikasa's corpse, Koichi and Rohan start investigating to find the culprit, who is ensured to be a Stand user. Later, Koichi runs into Takuma at the hallway in his high school, along with Josuke and Okuyasu, without realizing Takuma is the culprit and has already sensed their actions.

Enemies

 * Yoshikage Kira: Koichi, after learning of Kira's crimes, came to deeply loathe him to the point he would attack him on sight. Kira, on the other hand, came to somewhat praise Koichi's ability for being able to track him and then indirectly humiliate him in public, which he made sure to pay back with a beating. When Koichi humiliated Kira a second time, demonstrating how careless the serial-killer could be, Kira was enraged and came to detest Koichi, being happy at the prospect of Koichi dying.
 * Terunosuke Miyamoto: While there is little interaction between the two, Koichi hated Terunosuke for taking him hostage and trying to kill him and Josuke.
 * Polpo: While never meeting the man directly, he was attacked by his Stand and was shocked to learn he had an Arrow.

Chapters / Episodes
{{Appearance Part 4 =
 * Chapters =
 * {{Ch|Chapter 266}}
 * {{Ch|Chapter 267}}
 * {{Ch|Chapter 268}}
 * {{Ch|Chapter 274}}
 * {{Ch|Chapter 275}}
 * {{Ch|Chapter 276}}
 * {{Ch|Chapter 277}}
 * {{Ch|Chapter 278}}
 * {{Ch|Chapter 279}}
 * {{Ch|Chapter 280}}
 * {{Ch|Chapter 281}}
 * {{Ch|Chapter 282}}
 * {{Ch|Chapter 283}}
 * {{Ch|Chapter 284}}
 * {{Ch|Chapter 285}}
 * {{Ch|Chapter 286}}
 * {{Ch|Chapter 287}}
 * {{Ch|Chapter 288}}
 * {{Ch|Chapter 289}}
 * {{Ch|Chapter 290}}
 * {{Ch|Chapter 291}}
 * {{Ch|Chapter 292}}
 * {{Ch|Chapter 293}}
 * {{Ch|Chapter 294}}
 * {{Ch|Chapter 295}}
 * {{Ch|Chapter 296}}
 * {{Ch|Chapter 297}}
 * {{Ch|Chapter 298}}
 * {{Ch|Chapter 299}}
 * {{Ch|Chapter 300}}
 * {{Ch|Chapter 301}}
 * {{Ch|Chapter 302}}
 * {{Ch|Chapter 303}} {{Cover}}
 * {{Ch|Chapter 307}} {{Cover}}
 * {{Ch|Chapter 308}}
 * {{Ch|Chapter 309}}
 * {{Ch|Chapter 310}}
 * {{Ch|Chapter 311}}
 * {{Ch|Chapter 312}}
 * {{Ch|Chapter 313}}
 * {{Ch|Chapter 314}}
 * {{Ch|Chapter 315}}
 * {{Ch|Chapter 318}}
 * {{Ch|Chapter 319}}
 * {{Ch|Chapter 320}}
 * {{Ch|Chapter 321}}
 * {{Ch|Chapter 322}}
 * {{Ch|Chapter 323}}
 * {{Ch|Chapter 324}}
 * {{Ch|Chapter 330}}
 * {{Ch|Chapter 331}}
 * {{Ch|Chapter 332}}
 * {{Ch|Chapter 333}}
 * {{Ch|Chapter 334}}
 * {{Ch|Chapter 347}}
 * {{Ch|Chapter 348}} {{Mo}}
 * {{Ch|Chapter 349}}
 * {{Ch|Chapter 350}}
 * {{Ch|Chapter 351}}
 * {{Ch|Chapter 352}}
 * {{Ch|Chapter 353}}
 * {{Ch|Chapter 354}}
 * {{Ch|Chapter 355}}
 * {{Ch|Chapter 356}}
 * {{Ch|Chapter 357}}
 * {{Ch|Chapter 358}}
 * {{Ch|Chapter 359}}
 * {{Ch|Chapter 360}}
 * {{Ch|Chapter 361}}
 * {{Ch|Chapter 362}}
 * {{Ch|Chapter 363}}
 * {{Ch|Chapter 364}}
 * {{Ch|Chapter 365}}
 * {{Ch|Chapter 366}}
 * {{Ch|Chapter 367}}
 * {{Ch|Chapter 368}}
 * {{Ch|Chapter 369}}
 * {{Ch|Chapter 371}} {{Mo}}
 * {{Ch|Chapter 373}} {{Cover}}
 * {{Ch|Chapter 382}} {{Mo}}
 * {{Ch|Chapter 387}} {{Mo}}
 * {{Ch|Chapter 388}}
 * {{Ch|Chapter 390}}
 * {{Ch|Chapter 391}} {{Mo}}
 * {{Ch|Chapter 394}} {{Mo}}
 * {{Ch|Chapter 398}} {{Cover}}
 * {{Ch|Chapter 403}} {{Mo}}
 * {{Ch|Chapter 404}} {{Mo}}
 * {{Ch|Chapter 405}} {{Mo}}
 * {{Ch|Chapter 406}} {{Mo}}
 * {{Ch|Chapter 407}} {{Mo}}
 * {{Ch|Chapter 408}} {{Mo}}
 * {{Ch|Chapter 409}}
 * {{Ch|Chapter 412}} {{Mo}}
 * {{Ch|Chapter 414}}
 * {{Ch|Chapter 416}}
 * {{Ch|Chapter 417}}
 * {{Ch|Chapter 420}}
 * {{Ch|Chapter 422}}
 * {{Ch|Chapter 423}} {{C|Temporary death}}
 * {{Ch|Chapter 424}} {{Cover}}
 * {{Ch|Chapter 425}} {{Mo}}
 * {{Ch|Chapter 426}}
 * {{Ch|Chapter 427}}
 * {{Ch|Chapter 428}}
 * {{Ch|Chapter 431}} {{Mo}}
 * {{Ch|Chapter 435}}
 * {{Ch|Chapter 436}}
 * {{Ch|Chapter 437}} {{Flash}}
 * {{Ch|Chapter 438}} {{Flash}}
 * {{Ch|Chapter 439}}

Part 5
Part 6 =

Part 7
Part 4 = Part 5 = }}
 * Episodes =

Vento Aureo (PS2)
Koichi was planned to be in the GioGio PS2 game, likely as a playable character as there are beta pictures of him appearing in the game (such as one of him appearing with the main characters of Part 5 and in another one looking for Giorno and his stolen luggage). However, for unknown reasons Koichi was removed from the game, with no trace of him even in the game's Gallery Mode (unlike other characters, such as Risotto Nero or Leaky-Eye Luca, who do not appear in Story Mode but have viewable characters models regardless).

In canon Part 5, Koichi has a confrontation with Giorno over his stolen items and later helps him fight against Black Sabbath. As he was absent from the game, the Story Mode begins with the narrative skipping to Giorno on the tram being confronted by Bucciarati in Chapter 1, and in Chapter 3, Giorno fights Black Sabbath by himself.

All Star Battle (PS3)
Koichi makes his playable debut in the PS3 game and was confirmed along with Akira Otoshi. Koichi is voiced by Romi Park, who previously voiced Giorno Giovanna and Gold Experience Requiem in the aforementioned PS2 GioGio game.

Along with Enrico Pucci, Kosaku-Kira, Johnny Joestar, Hol Horse, and Giorno Giovanna, Koichi is a character who can utilize more than one Stand during a match as part of his moveset. In gameplay, Koichi uses all three forms of Echoes as part of his moveset, unlike Johnny or Pucci, who need to evolve their Stands during combat.

As one of the majority of playable characters with the "Stand" Style, Koichi can turn Echoes ACT3 on/off, changing movesets, as well as having access to the Stand Rush ability returning from the Capcom game, being able to attack in conjunction with his Stand.

During a fight, Koichi can use several different abilities that were featured in Diamond is Unbreakable. While Echoes ACT3 is off: While Echoes ACT3 is on: Koichi's HHA, GHA, or "S-H-I-T" inflicts 3 Freeze. The opponent is made heavier as a result of ACT3. This results in them moving much slower and being unable to jump for a period of time, forced into a constant crouch. While the effect cannot be broken by hitting Koichi or gaining enough distance, it has a relatively short duration, slightly altered based on the attack that generated it.
 * Throw - Whooooosh!: ACT2 hits the opponent with a "Whooosh!" SFX, sending them flying.
 * Enough!: Koichi runs forward and swings with all his might. If the punch connects, the opponent is sent flying upon impact. Koichi's skills can be performed instantly following this move. (Comboable)
 * I'll never forgive you!: Koichi summons ACT1 to fly forward and assault the opponent with loud SFX. This move has a follow-up. (Comboable through Puttsun Cancel)
 * Cicada's cry etched in stone: ACT1 increases the number and volume of SFX to the point where the opponent collapses. (Comboable)
 * Sizzle!: ACT2 throws its tail end in an SFX that arcs. If it hits the opponent, they will catch fire and gradually lose health over time for a few seconds. This move doubles as an anti-air. (Comboable through Puttsun Cancel)
 * Kaboom!: A counter. Koichi crosses his arms and glares, and if the opponent hits him during that moment, SFX by ACT2 will reveal itself on Koichi and they will be blown back.
 * Boing!: ACT2 slaps an SFX on the ground in front of Koichi. If the opponent comes in contact with it, they'll be blown upward into the air and take slight damage upon landing (Comboable). If Koichi himself touches it, he will leap high into the air, allowing him to evade many of the opponent's attacks or set up his own attacks from the air.
 * Hit them, ACT3!: ACT3 flies forward, rapidly punching the opponent and pushing them away. (Comboable through Puttsun Cancel)
 * S-H-I-T: ACT3 flies into the air and comes down punching with the 3 Freeze effect active, downing the opponent. This move doubles as an anti-air and inflicts the 3 Freeze effect for a short duration. A Stand Rush skill that Koichi can disconnect from to attack the opponent while it is executing. (Comboable through Puttsun Cancel)
 * This air pressure?!: ACT3 swiftly moves in front of Koichi and unleashes an intense burst of air capable of knocking both him and the opponent back. This skill can interrupt an opponent's combo, and unlike other skills of similar effect, does not spend any amount of the HHG. However, Koichi is harmed as well for even more damage. Koichi may recover up to half of the lost health over time, but only if he does not receive any more damage during the process.

Koichi's HHA, "Echoes ACT3: FREEZE!!", sends ACT3 flying forward, rapidly punching the enemy with the Freeze effect active and pushing them away for an extended period of time, with the final hit knocking them down. The HHA does not require an initial hit to connect in order to work, and will not stop until it finishes or Koichi is interrupted. The HHA inflicts the 3 Freeze effect for a medium-length period of time.

Koichi's GHA, "I'm really getting stronger?!", starts with him summoning ACT1 to throw a "BAM!" SFX. If it lands, the opponent is assaulted by SFX loudly repeating itself enough to make them cover their ears. ACT2 flies in and places a "KaBOOM!" SFX under them, blasting them high into the air. The GHA finishes with ACT3 appearing above the opponent and performing a barrage of punches while activating 3 Freeze, making the opponent smash into the ground on landing. The GHA inflicts the 3 Freeze effect for a long period of time.

Aside from being a playable character, Koichi also appears on the stage "Kira Estate" as a background character, if he himself is not one of the two fighters, along with Okuyasu. Koichi also appears as the auto-save icon, with his face under the effects of Heaven's Door as the pages flip.

Koichi uses unique dialogue before a fight with Jotaro or Giorno, telling the latter that he wants his suitcase luggage back, recreating their antagonistic dynamic during early Part 5 before they leave on good terms.

Koichi possesses two alternate costumes, the first being the pajamas he wore during Yukako's introductory arc and his second one being his T-shirt with the LUCKY.CO logo on it that he wore during his assistance in Josuke's battle against Highway Star.

Koichi also won the first place in his League Group in the All Star Battle League, beating fan favorites such as Giorno, Jolyne, and Gyro. He even managed to reach to the semi-finals matches, but ultimately lost to Jotaro.

Eyes of Heaven (PS3/PS4)
Koichi was confirmed for the game alongside Yukako.

Once again Koichi is voiced by Romi Park and his main color scheme is the same from the previous game.

Since most of the game's animation, effects, and attacks were reused from All Star Battle, Koichi's style of play remains mostly the same; focusing on using a variety of abilities across Echoes' different ACTs.

As a Stand User, Koichi is one of many characters with wildly varied abilities that grant him uniqueness in battle.

While ACT1 is active:
 * Style Action - ACT1/ACT2/ACT3: Koichi cycles Echoes through its different ACTs, completely changing the skills and attacks available to him. Each ACT specializes in a certain area: ACT1 grants useful buffs and debuffs despite its low attack and skill count; ACT2 focuses on ranged attacks and traps, being able to throw its tail as a projectile in exchange for melee; ACT3 grants access to normal melee combos and conventional moves involving its punches and 3 Freeze.


 * Trust me!: ACT1 throws an SFX with some homing capabilities at his partner, and if it connects, they are granted a boost in stamina and the Dual Heat Gauge is filled by a small amount. This skill is unavailable if Koichi's partner is out of range. If partnered with Yukako, the skill's effectiveness is increased.

While ACT2 is active:
 * I hate you!: ACT1 throws an unblockable SFX with some homing capabilities at an opponent, and if it connects, the target's defense and stamina gauge is lowered, and the enemy team loses an amount of their own Dual Heat Gauge. If fighting against Yukako, she is immune to this effect while her "I can't hear you!" passive skill is active.


 * Boing!/Whooooosh!: The attack unleashed is dependent on whether or not the movement stick is tilted in a direction while the skill is inputted. If inputted from neutral, ACT2 slaps an SFX on the ground in front of Koichi. If an opponent comes in contact with it, they'll be blown upward into the air taking no damage. If Koichi himself touches it, he will leap high into the air, allowing him to evade many of the opponent's attacks or set up his own attacks from the air. If inputted while moving, ACT2 instead swings its tail horizontally, placing a different SFX on a wall (of note is that the in-game description erroneously claims the surface to be the ground) if available or dealing small damage to an opponent in-range otherwise. If an opponent comes in contact with the SFX, they'll be blown backward a great distance, still taking no damage.


 * Sizzle!: ACT2 utilizes an offensive SFX from its tail to catch opponents on fire and cause them to gradually lose health. The execution of the skill is dependent on whether or not the movement stick is tilted in a direction when it is inputted. If inputted from neutral, ACT2 throws the SFX in a straight line with an indefinite range as a projectile. If inputted while moving, ACT2 slaps the SFX on the ground where it becomes a trap. If the skill is executed in the air, the projectile version is performed by default.


 * Bahyoo!: ACT2 whips its tail outward with it semi-transformed into an SFX. If it connects with an opponent, they take moderate damage and are sent flying a large distance away.

While ACT3 is active:
 * EX - Sizzle!: The SFX gains a damage boost, and the projectile version of the skill flies faster.


 * 5-METER RANGE ACHIEVED. S-H-I-T!: ACT3 generates a short gravity field around itself, dealing a small amount of damage to opponents and immediately downing them. This inflicts 3 Freeze's effect, dubbed Heavy. Once in effect, targets will be unable to jump, and their movement speed is much slower for a period of time. Similar to All Star Battle, if Heavy is inflicted on Kira's Sheer Heart Attack, it will be immobilized for a period of time.


 * Echoes 3 Freeze!: ACT3 flies forward, unleashing a barrage of 8 punches and pushing opponents away while inflicting Heavy.


 * Wh-What is this wind?!: ACT3 swiftly moves in front of Koichi and unleashes an intense burst of air capable of knocking both him and the opponent back. This skill is unblockable and creates a large amount of distance if successful. However, Koichi is knocked down and takes a small amount of damage in the process.


 * EX - 5-METER RANGE ACHIEVED. S-H-I-T!: The duration of the Heavy effect inflicted is increased.

JoJolities

 * Trust me!: Koichi must connect "Trust me!" twice. (200 Points)


 * You're no match for Echoes ACT2!: Koichi must connect "Sizzle!" twice.(200 Points)


 * My ACT3 is awesome!: Koichi must inflict Heavy 3 times. (300 Points)


 * ACT3 Freeze!: Koichi must perform a Dual Combo Finish. (500 Points)


 * I have protected you as ordered.: Koichi must Retire an opponent with a Dual Heat Attack. (800 Points)

Dual Heat Attacks

 * Solo - I'm really getting stronger?!: Identical to its performance in All Star Battle, though executes faster for the sake of brevity. It also still inflicts Heavy afterward.


 * With Josuke - Dorara Rush ×2: Koichi has Echoes ACT2 place SFX of Crazy Diamond's Stand Cry ("DORARARA!!") directly under the opponent's feet. He then prompts Josuke to attack, watching as he jumps high into the air until he is directly above the opponent. The SFX then activates, creating artificially-made fists to attack from below as Crazy Diamond punches the opponent from above, hitting them from both sides. This is the only DHA available to Koichi that does not involve 3 Freeze and therefore does not inflict Heavy.


 * With Yukako - Invincible Heroine: Koichi uses 3 Freeze to make the opponent heavier, then Yukako wraps them in her hair before attempting to fling them around. Despite struggling with the increased weight of the opponent, she successfully slams them into the ground four times before raising them extremely high up into the air and launching them into the ground one more time hard enough to generate a shockwave.


 * With Rohan - We're best friends!: Koichi uses 3 Freeze to make the opponent heavier, before Rohan uses Heaven's Door to write in the opponent "My weight will increase 10-fold.", combining the effects and multiplying their weight to such a degree that it causes them to slam face-first and sink into the ground with enough force to generate a crater.

In the post-credits scene of the new JoJo timeline where most of the fallen allies (including the actual Kosaku Kawajiri) are now alive well (and Joshu's relationship Part 8 Josuke improves), during the retelling story of Part 4's first chapter where he met Jotaro, Koichi claims to experience deja vu, and that he met a younger Jotaro somewhere before.

Tournament
He is paired with Will A. Zeppeli in the Eyes of Heaven Tournament but was eliminated in the preliminaries by Jonathan Joestar and DIO.

Last Survivor (Arcade)
Koichi was one of the characters first confirmed during the game's announcement.

Gallery
Manga=

Trivia

 * Koichi's name and basic appearance appear to have been taken from the main character and a narrator of one of Araki's earlier works, Cool Shock B.T. GIKoichi.png
 * Koichi's surname, "Hirose," is derived from the Hirose River (広瀬川), located within the city of, Araki's birthplace.
 * Although it's never been explained why, Koichi's enemies tend to shrink in size after he beats them. This is not shown in the anime for consistency; Koichi's enemies are already short when they're introduced.