He is the little brother of Act-Age main protagonist Kei Yonagi. He was born with a twin sister, Rei Yonagi. Unlike his twin sister, he isn't afraid of Yonagi's behavior. He just sometimes thinks that Yonagi's acting is weird. He is still a crybaby, it is even harder to calm him down once he starts crying. He is a fan of Ultra Masked Man, a fictional character played by Akira Hoshi.