Birthday: November 16
Yuuichi is a member of Fuuka Academy's Student Council. He first appears in Episode One on the same ferry as Mai Tokiha, and they quickly form negative impressions of each other. Shiho Munakata calls him her older brother despite not being related by blood. Yuuichi works with the Student Council, doing various tasks for them, leading Mai to label him a "lackey." He also sits next to Mai in class.
Yuuichi used to be part of Fuuka's kendo club and regularly competed in nationals until he suffered a severe knee injury in the past. The exact circumstances and nature of the injury are never explained in the anime. Masashi Takeda from the kendo club is seen looking sadly at Yuuichi's name card on the dojo wall during the series. After his injury, Yuuichi became a feared delinquent but was convinced by Shiho to give up his antisocial ways.
Despite their initial dislike, it becomes clear that Yuuichi has feelings for Mai. Their attitudes towards each other soften after episode 5 when Mai breaks down and is comforted by Yuuichi. He witnesses Mai about to kiss Reito Kanzaki and tries to interfere, much to Shiho's distress. After Shiho is attacked by a SEARRS Orphan, Yuuichi becomes suspicious about recent events at the school and urges Mai to tell him what's happening.
When the insecure and possessive Shiho realizes that Mai and Yuuichi are developing feelings for each other, she becomes mentally unstable and forces Yuuichi to kiss her in front of Mai, exploiting his guilt over failing to protect her. Yuuichi becomes the Most Important Person for both Mai and Shiho, which leads to his death when Shiho's Child is killed by Mikoto. Just before disappearing, Mai confesses her feelings for him and tries to kiss him.
Yuuichi is later revived by Mashiro Kazahana and comes to Mai's defense using Miyu's discarded sword when the possessed Reito attacks her. Yuuichi vows to protect Mai and declares his love for her, much to Mai's relief. However, at the end of the series, both Mai and Yuuichi are still pursued by Reito, Mikoto, and Shiho.
In the manga, Yuuichi is the protagonist and the transfer student instead of Mai. He discovers he is the Key to both Mai and Natsuki, two rivals at the school, intensifying their mutual animosity. Due to his dual Key status, he is often called a 'Perverted Beast' by his classmates. His relationship with Mai mirrors the one in the anime but includes further complications involving Natsuki.
Yuuichi was dismissed from his former school's kendo club after attempting to stop the sexual assault of Shiho, resulting in his team's disqualification from championships. During the assault, he received a long gash on his left arm from a knife. This injury makes him extremely sensitive about joining Fuuka's kendo club, despite the captain's insistence.
