- Keiji Sendai (千代 啓二, Sendai Keiji?)
Voiced by: Shintarō Asanuma (visual novel)
Keiji is Yūto's classmate; he is known as "mad dog". He calls himself a "natural enemy of Akiba-kei, though Yūto has seen him in Akihabara and at Comiket. He originally comes from Shaa's other manga series Kyōhaku Dog's. He only cameos in the anime.