Yukako Yamagishi

Yukako Yamagishi (山岸由花子) is a supporting character and Stand user in Part IV: Diamond is Unbreakable.

Appearance
Yukako is a teenage girl of fine build, 167 cm (5'5¾") tall. She is characterised as especially beautiful (noted by Aya Tsuji ), with fine facial features and bodily proportions; full, wavy, dark, glossy, roughly waist-length hair; and dark eyes. She usually wears a dark seifuku, while displaying mature taste in casual clothing.

Personality
Yukako is a high school student. She is introduced in the midst of a date with Koichi Hirose, whom she quickly reveals to be her singular and obsessive love interest, which subject occupies the majority of her role in the story.

Aloof, she expresses a casual contempt for people in general. With the power of her Stand she is able to act aggressively on an intense possessiveness towards Koichi, becoming violent towards any who she feels would hurt her chances of captivating him. She takes an overtly psychopathic turn when she opts to kidnap and indoctrinate Koichi, before his triumphant escape.

Later, during her trials by the mysterious beautician Aya Tsuji, she manages to evidence an integrity to her desire for Koichi, finally motivating his reciprocation and neutralizing her unease.

In terms of archetype, Yukako may be described as yandere. Araki comments that her personality was designed in reaction to a prevalent moe perfectionism to female characters, and in the statement that someone of any gender should be capable of being frightening or losing their temper.

By her basic characterization and the conventions of Horror exploited through her during her first storyline, Yukako also holds parallels to the story's primary villain, Yoshikage Kira.

Diamond is Unbreakable
At first, Yukako is shown as being in love with Koichi Hirose. Very aggressive in her affections towards him, jealously attacking what she believed were potential rivals in love and even going so far as to kidnap him and threaten his life should he not return her feelings and not appreciate her efforts to "change him into a better person" – she had picked up false rumors that were spread by Josuke and Okuyasu in order to help Koichi turn her away from him; unfortunately for them, their measures had the opposite effect. Koichi then was forced to fight against her, but saved her life soon after. Akira Otoishi reveals to Josuke that she was one of the stand users he was watching with his Red Hot Chili Pepper. Later in the story Yukako is warned about Yoshikage Kira after Shigekiyo Yangu's death and advises everyone to be careful.

Yukako, still lovestruck, seemed to have learned from her mistake in trying to force Koichi. Unhappy about her unrequited love she made use of the services offered by Aya Tsuji's beauty enhancing Cinderella stand, which rendered her into a bewitchingly attractive woman in the eyes of Koichi - for a price and a certain time limit, during which she was to use a special lipstick in order to uphold the "magic" i.e. the stand's power. The stand allowed her to grow closer to Koichi, who, after some trials and tribulations, warmed up to her and willingly became her boyfriend.

However, when she forgets to apply the magic lipstick, her face becomes deformed and she flies into a rage at Aya, who grants her a chance for her to return to her original appearance should she be able to pick her original eyes. Yukako has trouble picking the right one until Koichi arrives to her aid and decides that he will pick for her, but requesting Aya that she take away his eyes should he make a mistake. Aya, unwilling to take the role of an antagonist, decided to give Yukako her original appearance back. Yukako last appears to give goodbye to Reimi Sugimoto.

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 consideredcanon.)

Yukako was Chiho Futaba's neighbor when they were kids. She helps Koichi find Hanae Orikasa's killer, a student with red marks on his arms. Suspecting the killer might be in the same class as them, Yukako traps their class in the classroom so Koichi could rise the temperature with a word made by Echoes, making the students take of their jackets. Unfortunally, the killer wasn't in there.

Trivia

 * Okuyasu Nijimura seems to be a secret admirer of hers.
 * Her Stand's ability, the manipulation of her hair, is very similar to that wielded by Bruford.
 * Yukako is the first female ally in the series to wield a Stand.
 * An image of Yukako from Chapter 350 is featured on the limited edition cover of Base Ball Bear's 2009 single "Breeeeze Girl", as well as on billboards for its promotion.