Yukino and Soichiro's lazy and girl-crazy friend, very handsome and popular. Although bright enough to be accepted to the selective Hokuei High School, Hideaki is a terrible student, and spends most of his time surfing or chasing girls. Hideaki and Soichiro are considered the two most handsome boys in school, and while Soichiro is largely indifferent to the attention, Hideaki makes the most of it. During their school's annual culture-fest, Hideaki's class mounts a "Hideaki Asaba Dinner Show" which is a big hit with all the girls, but gives Yukino and Soichiro the creeps.
He initially tries to become friends with Soichiro so that Soichiro can be his "wingman" as they chase girls together. To this end, he tries to break up Soichiro and Yukino, because Yukino is in the way of Hideaki's dream of "Mary-land" (a land full of girls). When Soichiro finds out about this, he becomes very angry at Hideaki. Hideaki also has a series of hilarious battles with Yukino, since Yukino is not one to back down from a challenge. Although things started out badly, the three of them eventually become good friends. (Yukino calls him "Asa-pin".)
While an outrageous flirt (he dares to hit on Yukino's mother ... in front of Yukino's father!) and goofball, he has his own dark past—he is estranged from his parents. He is also one of the few people who understands Soichiro's dark side. In fact he frequently states that he would love to marry Sochiro, if only Sochiro was a girl instead. During Yukino and Soichiro's relationship crisis during their senior year, Asaba tells her that only she could reconcile Soichiro's heart.
Later on, Hideaki becomes a famous painter, earning the title of "Takehisa Yumeji of the Heisei Era". (Yumeji is a famous Japanese painter during the Meiji era. Also of note is that his mentor is Soichiro's maternal grandfather.) True to his woman-loving nature, he specializes in drawing female portraits, and makes the subject of the portrait five times prettier. Maho realizes that this is because Hideaki truly sees women to be five times prettier than they actually are — which explains why he is so in love with all of them. (However, it is interesting that Yukino is the only woman who looks the same, and not extra-beautified, in Hideaki's portraits.) Despite loving women in general, Hideaki has never settled down or married; he feels empty inside and continues to feel as if he's missing something.