Rio is a first-year university student taking up Political Economics and the keyboardist for the band Argonavis.

Rio excelled at everything since his childhood and was called a "child prodigy." He hoped to be a baseball player in the future, but right before he was able to participate in Koushien, he was injured, and he abandoned that path. Although he doesn't reveal his emotions, seems apathetic to people, and doesn't get close to anyone, he responded easily to Yuto's scout. Since joining the band, he has been giving his all. He's also the son of the director of a famous confectionery company in Hakodate.