Seiichirou Minamoto is a high school student in the third year. He is known for his interests and is considered by many to be fellow and junior interests. His favorite fanatic is Cinnamoroll. But not only does he love Cinnamoroll, he loves his friends too. He does archery(captain), and is the student council representative also known as the president. He is 1 of the original 5 members of the Sanrio boys friend group. 

Seiichirou is manly besides the fact he loves something so soft as Cinnamoroll. He likes to do archery and became the captain of the team he is strong with a nice build. He is academically smart and level-headed those are just some of the reasons he is the schools student council main representative. In the friend group he is the most mature. And he is the closest to Ryo Nishimiya a smaller, shyer boy in school. We are introduced to him(Seiichirou) in ep.5 when help the boys out when Nishimimya got mad at them for talking about "something so girly" out loud. He is quick to stop fights, very kind, for others, and is some what of a perfectionist.