Birthday: November 16
Yuuichi is a member of the Fuuka Academy Student Council. He first appears in Episode One on the same ferry that Mai Tokiha is taking and the two quickly form bad impressions of each other. Shiho Munakata calls him her older brother even though they are not related by blood. He works with the Student Council doing odd jobs for them (prompting Mai to label him a "lackey") and sits next to Mai in class.
Yuuichi used to be a member of the Fuuka kendo club and regularly made it into the nationals until he was suffered a severe injury to his knee at some point in the past, though the exact circumstances and nature of the injury are never explained in the anime. Masashi Takeda of the kendo club is seen looking sadly at Yuuichi's name card on the wall of the kendo dojo at one point during the anime. Disenchanted, after his injury Yuuchi became a feared delinquent, but Shiho manages to convince him give up his antisocial ways.
In the manga, Yuuichi is the protagonist and the one who is the transfer student rather than Mai. He finds out that he is the Key to both Mai and Natsuki, two well-known rivals at the school, exasperating and intensifying their mutual antipathy. Because of his dual Key status, he is often referred to as a 'Perverted Beast' by his classmates. His relationship with Mai is much like the one in the anime, although there are further complications. i.e., Natsuki.
Yuuichi was forcefully dismissed from his former school's kendo club after he attempted to stop the sexual assault of Shiho, costing his team the championships because of their disqualification. During the assault, one of the roughnecks pulled a knife out, and gave him a long gash proceeding from his elbow down to his wrist on his left arm. He is extremely sensitive about it, and it is the reason he refuses to join Fuka's club despite team captain Takeda's insistence.