Seiichirou is a young man with short black hair and red eyes.
Seiichirou deeply cares for his friend Natsusa and would always visit him and help out as much as he can. He doesn't really want Natsusa to push himself due to his injuries, but will always be there for him to support him if he needs.
Seiichirou had spoke with Natsusa's mothers as he didn't call her, although she mostly spoke about her favorite idol group disbanding than Natsusa. On the next day, he went to pick Natsusa and it was his first day at school after his accident.
Later when Natsusa decided to become a manager, Seiichirou told him the job required physical work and that he may injure himself, but as Natsusa was serious, he decided to support him.