Koutarou is a truant sophomore in Kagami Junichiro's class in Ichou Academy. He went to the same middle school as Fries (Shikishima Kiriko) and heard an odd rumor about him. He has never appeared ever since the school's opening ceremony. He is a hikikomori.
He is actually Luce, The Ironclad Sister and Kagami's Uroboros RPG partner. His addiction to everything cute since his childhood made him keen on collecting cute things, as well as wear them. Despite being a guy, he resembled his avatar very much, looking like a real girl to those who don't know his identity. During middle school, he tried to walk out of his house wearing girly clothes, but ended up accidentally hospitalizing a classmate who discovered his secret hobby and since then he was not only afraid to leave his home, but also meet other people and question his gender/identity. In the end, Kagami was able to convince Koutarou to reveal his true identity to his classmates after a final match with First (Kagami's character) which ended in his victory. Koutarou has returned to school, and his classmates accepted him as what he really is. He was also given permission to wear a girl's uniform and was FORBIDDEN to wear the male uniform.