Kotoōshunus is a gladiator active in ancient Rome during the period of Emperor Hadrian, appearing in the narrative of Thermae Romae II. He belongs to the so-called "thick face tribe," a comedic designation used in the story to distinguish characters with strong, non-Japanese features from the Japanese "flat face tribe." His name is a humorous reinterpretation of the sumo wrestler Kotoōshū. In the story, he participates in gladiatorial combat in the Colosseum and later comes into contact with the innovative bathhouse built to heal and restore wounded fighters. The character is not given extensive personal background or notable development, functioning instead as a secondary figure who supports the film's lighthearted portrayal of Roman culture. He is depicted as physically powerful and capable in battle, but his inner personality and deeper motivations remain unexplored. His primary narrative purpose is to illustrate the interaction between Roman customs and Japanese-inspired bathing concepts within the gladiatorial setting.