The Judo Club is a club at Saotome High School. Members include Ozuma and his friend, Satou.
Mikiri is also an unoffical member, disguising herself as "Master" or "Judo Mask". The members say that they don't know who their master is, but knows her "body".
Satou seems have gotten their master's identidy partially right. After seeing Motoko (as Hibiki) fight he suspects Motoko to be their myserious teacher.