Hayato Kawajiri

Hayato Kawajiri is a character in Part IV: Diamond is Unbreakable. He is portrayed as an ally to the protagonists and plays a crucial role in the last arc of the story.

Personality
A schoolboy with a knack for science, Hayato tends to spy on his parents with his home-built electronic devices, finding interest in their affairs and conversations.

However, when pressed into a corner, Hayato can prove to be exceptionally brave. Even Josuke has commented on Hayato's bravery when he volunteered to set off Okuyasu's explosively-charged body at the risk of death, and expressed surprise that he was a grade school student.

Diamond is Unbreakable
During his usual routine of spying on his parents with electronic devices, Hayato notices several highly suspicious things about his father Kosaku, who at the time was being impersonated by Yoshikage Kira, and is nearly killed by Stray Cat when he investigates. He begins following Kira with a video camera, and manages to record footage of him murdering a woman and her boyfriend. When he is cornered by the murderer, he attempts to blackmail Kira by revealing that he has further evidence that will be found by authorities in the case of his death, but his threats only anger Kira, who uses Killer Queen to dispatch him. Immediately after, Kira begins to panic, and is spontaneously pierced by the Bow and Arrow. With his new ability, Bites the Dust, he activates a time loop that restores Hayato to life.

The next morning, Kira gloats to Hayato over his new ability, revealing his true name in the process, as well as the fact that his ability is "invincible." Hayato deduces from this that there are others with similar abilities. Immediately after Kira leaves him, Rohan Kishibe, who has seen him following his father to the train station, uses the power of Heaven's Door on him to learn the identity of his father. Rohan becomes the first to fall victim to Killer Queen's Bite the Dust ability. He then wakes up in bed again, having experienced it in a "dream sequence", and realizes that he is trapped in a time loop. On this morning he attempts to avoid Rohan, hoping to find the other ability users and get their assistance, but is only able to watch Rohan die from a distance as Kira explains the effects of his Stand. He attempts to avoid Josuke and company, but is accosted by them and tries to hold Bites the Dust off by killing himself with a box cutter. However, Bites the Dust activates, this time to protect him, killing Josuke and his friends.

Upon waking up in his bed again, Hayato realizes that he can only rely on himself to unmask Kira. He then exploits the time loop, this time to his advantage, and successfully steals Stray Cat, hoping to use his knowledge of the morning's events to defeat Kira at close range. His attempt nearly succeeds, but Kira is protected from Stray Cat's air bullets by a watch in his pocket. As Kira gloats in victory, Hayato is saved when his secondary plan succeeds in making Josuke Higashikata and Okuyasu Nijimura arrive in time to hear Kira reveal his own name. When Josuke attacks him, Kira is forced to recall Killer Queen to protect him, canceling the effects of the time loop.

During the battle, Hayato plays a major role in assisting Josuke and Okuyasu as a tactician. When Okuyasu is mortally wounded and Josuke conflicted over whether to risk being blown up by using Crazy Diamond's ability to save him, Hayato throws himself at Okuyasu and sets off the bomb. However, this sacrifice does not lead to his death, as Josuke pieces his body back together before he is able to die from being blown apart. When he follows Josuke and they all take shelter in a house, Hayato discovers a photo of Yoshihiro Kira spying on their location in his jacket pocket, enabling Josuke to eliminate Yoshikage's last support. Hayato is among the group of people to witness Yoshikage Kira's death, and is last seen tearfully telling his mother Shinobu Kawajiri he would wait for his father to come home, even though Hayato knows that he is already dead.

Jojo's Bizarre Adventure: All-Star Battle (PS3 Game)
Hayato Kawajiri appears on the game as part of Kosaku (Kira)'s GHA. Kira grabs Hayato and throws him at the opponent saying "Killer Queen Third Bomb!" If Hayato manages to hit the enemy, the camera zooms into the opponent's eye, where Killer Queen appears and detonates the time bomb. The round timer rewinds ten seconds and Kosaku regains some health. If the opponent has gone through a transformation (Gold Experience Requiem, Made In Heaven, any Steel Ball Run character with the 3 corpse parts or Kars's Ultimate form), they are reverted back to their original forms. However, if the opponent manages to avoid or defend the attack, Hayato will run away from the screen.

Hayato also appears as a memo book for the Special Edition of the game (called Gold Experience Edition), where the book contains information such as character profiles and manual guide. The special edition also contains a code to freely unlock the character Yoshikage Kira.