His mother passed away shortly after his birth, leaving him in a predominantly male environment during his childhood. Consequently, he felt overwhelmed by girls due to his lack of experience with them. His father was a musical conductor, and all three of his brothers were skilled at playing the violin and cello. In contrast, Yasuaki was highly athletic and enjoyed surfing. Hanabi assumed that Yasuaki had no interest in pursuing a musical career because he preferred surfing, which he confirmed. However, she later discovered that he played the piano exceptionally well. He revealed that to continue surfing, he had to pass his father's piano test whenever his father returned home. One day, he took Hanabi to his house where she met his strict father and flirtatious brothers in an effort to gain their approval for their relationship.
Yasuaki lived alone most of the time, just like Hanabi. He frequently cooked dinner for both of them since Hanabi usually ate junk food. During junior high school, he attended an all-boys school, continuing this trend into the early years of high school. As a student council member, the most popular boy in school, and talented at surfing among other activities, he was essentially an ideal boyfriend. He still referred to girls as "chicks," except for Hanabi, whom he viewed as a game fowl. Nevertheless, Yasuaki and Hanabi eventually began dating. He became very serious about their relationship, even hinting at marriage. He also adopted some techniques and lines from his older brothers to use on Hanabi.
However, his jealousy flared when he met Takeru Suno, Hanabi's childhood friend. Their close bond led Yasuaki to confront Takeru, resulting in a fight where he was severely beaten. Despite this, Hanabi chose Yasuaki, and after overcoming various mishaps and misunderstandings, they grew closer. By book five, they had become intimate, curing Yasuaki of his "girl allergy" and enabling him to see girls instead of chicks. Hanabi shared that she might like Yasuaki because he was unexpectedly sweet.
