Ren is one of the three Sanada demons, extremely powerful ninjas, who acts under the guidance of Misanagi, the leader of the Sanada. He fights alongside his comrades, when Himura Kenshin and his friends, assisted by a former Sanada member, attempt to thwart the plans of Misanagi.

He encounters Himura Kenshin their battle, he is able to render useless one of Hiten Mitsurugi-ryuu's moves, using a move of his own called "Death Run." This appears to be the only move Kenshin can perform, since he is unable to get inside Ren's range, due to a spell used by Baku's bats.