His mother died very shortly after he was born. As a kid, he was surrounded by men and had no experience with girls. As a result he became rather overwhelmed by girls. His father was a musical conductor and his three brothers were all proficient at the violin and cello. However, Yasuaki was incredibly athletic and loved to go surfing. Hanabi guessed that Yasuaki had no interest in pursuing the musical profession because he would rather surf, which he agreed with, but she soon discovered that he plays piano very well. He told her that in order to keep surfing, he must pass his father's piano test every time his father comes home. He even took Hanabi to his home one day where she met his stern father and playboy brothers in order to get them to approve of their relationship. Yasuaki lives alone most of the time, just like Hanabi. He would often cook dinner for Hanabi and himself, since Hanabi usually eats junk. In junior high school, he used to go to an all-boys school, which followed through the beginning of his high school years. As a student council member, most popular boy in the school, and good at surfing among other things, he's basically an ideal boyfriend. He still sees chicks instead of girls, with the exception of Hanabi, who he saw as a game fowl. However, soon enough, Yasuaki and Hanabi start to date. He becomes very serious about Hanabi, even hinting at marriage. He also picked up some techniques and lines from his older brothers, using them on Hanabi. But it isn't long before he meets Takeru Suno, a childhood friend of Hanabi but the two's closeness causes Yasuaki to go into a fit of jealousy, and pick a fight with him. Even though he got severely beaten up in the fight with Takeru, Hanabi still chose Yasuaki and after other mishaps and misunderstandings they begin to get closer, and in book five they even get intimate. This cures him of his "girl allergy" and allows him to see girls instead of chicks. Hanabi shares that perhaps she likes Yasuaki because he is sweet when she least expects it.