Mugen is rude, vulgar, and often thinks highly of himself. Much of his past is a mystery. He was born on the Ryukyu Islands, never knew his parents, and was a former pirate. After an incident forced him to fake his death, he became a vagabond. But things changed after he met Jin and Fuu. Though very rough around the edges, he has a mutual understanding with Jin and cares for Fuu more than he lets out, considering he usually ends up going after her whenever she gets kidnapped. His fighting style is described as a "champloo," which means "mix." It combines all sorts of martial arts, unorthodox swordplay and break dancing. He relies on instinct and reflex to surprise his enemies. His style of clothing represents the future, whereas Jin's represents the past. His black hair is usually untidy, and is similar in shape to an afro.

She is a college student at Nerima University who is majoring in Literature. She currently lives in Room 204 of Royal Hills Nerima. She works as a rental girlfriend for an agency called Diamond under the alias Chizuru Mizuhara (水原 千鶴).