Coo is 13 years old and the Major of the Black Gema Gema Gang. He is the physician of the group. He is Piyoko's childhood friend and is closest to her. Sometimes if food flies through the air he will jump up and catch it in his mouth in a dog-like manner. As the gang considers themselves a "family," Coo is considered the "brother"; however, Piyoko thinks she is older than him, although she is only 8 while he is 13.