The self-proclaimed childhood friend of Masato Kataoka who affectionately calls him "Maa-kun." Yuki strives to live like a girl, and moves to Tokyo with the hope that she can make a fresh start with her new life. She moves into Masato's apartment and begins attending Masato's high school wearing a girl's uniform. Yuki quickly becomes popular among her peers, and no one is aware that she is actually male. Even the teacher, Mizutani-sensei, who begins living with Yuki and Masato, does not realize it. Although claiming that he is not a homosexual or bisexual, Yuki bluntly states that he is in love with Masato because of how kind she was to him when they were kids. She constantly wears a Hello Kitty pendant that she claims Masato gave to her, and reminisces about their childhood together often.

Spoiler

The "Maa-kun" that she holds so dearly to her heart is not actually Masato Kataoka, but rather Masato's girlfriend Kaoru. As a child, Yuki mistook Kaoru for a boy due to her tomboyish appearance and behavior.