Is a boy who Eri fell in love with, shortly after joining Seiji's school. According to a friend of his, who is also a boyfriend of one of Eri's friends, boys don't like it when the girl they are with are virgins, leading Eri to try and seek out a trust-worthy boy to take her virginity.
Having caught Seiji leaving a Love Hotel with her friend Yuki, Eri decided to get Seiji to take her virginity. Upon being caught by Shou, the two later meet again and Eri begins explaining her motive. Feeling that Eri is like him, but only more desperate, Seiji helps Eri get the courage to confront her love-interest, only to learn that he likes someone else. He doesn't state whether it is his girlfriend or not.
Fortunately, the two part happily, and from then on, Eri becomes grateful and pleased with her 'new path'.