Yukako Yamagishi

Yukako Yamagishi (山岸由花子) is a fictional character from Part IV: Diamond is Unbreakable.

Appearance/Personality
Yukako is a high school student whose hair reaches down to her waist. She is shown to have a intense personality full of assumptions, attacking girls she deemed as rivals without any proof. Yukako is particularly a selfish and determined person, especially when considering her love interest Koichi Hirose. This determination translates into various actions, from aggressively attacking potential rivals in love to forcibly correcting Koichi to make him a better person, and even requesting the services of Aya Tsuji to make her more attractive to him. She is also described as being non suspeticious and over energetic.

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 a nighborhood of Chiho Futaba 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 her.
 * Her house is located at the edge of Morioh-cho, right by the cliffs of the sea.
 * She use her stand to manipulated her hair like the zombie Bruford.