is a 19-year-old man who is one of the main protagonists of the series. He was born in a penal colony on the Ryukyu Islands which in the Edo period was a separate kingdom with close ties to Japan's Satsuma domain. Incidentally, Mugen writes his name using the infinity symbol (∞), a pun on his name, which is a homophone of the Japanese word for "infinite". His Japanese is quite rough and "Yankī"; and he is illiterate until later in the show. Little is known about Mugen's childhood and he states that it has been a long time since he can remember what it is like to have parents in episode 20, "Elegy of Entrapment, Verse 1". The blue tattoos on his wrists and ankles indicate that he was once in prison. The circumstances of his imprisonment are initially unclear, but it is later verified that he was to be executed for engaging in piracy.