Seiichirou is also the treasurer of the student council, along with his sister Shiro. He is very kind with his sister, and may have a sister complex. He used to be the president of the Japanese archery club. Also, has a bitter temper. It is later revealed that he is servant of Iori. He even reveals to Kohei that Erika is his blood sister who was given away to Sendou family on Kaya's request.