Ren is one of the 3 Sanada demons, extremely powerful ninjas, who act under the guidance of Misanagi, the Okashira (leader) of the Sanada. He fights alongside his comrades (the other two demons), named Zan and Baku, when Himura Kenshin and his friends, assisted by a former Sanada member, named Kaita, attempt to thwart the plans of Misanagi. He encounters Himura Kenshin their battle, he is able to render useless one of Hiten Mitsurugi-ryū's moves (Doryūsen), 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, which effects Kenshin's five senses, making him see illusions as soon as he gets near Ren. As a result, Ren manages to grap hold of Kenshin's neck and right hand with his whips. However, after Kaita tells him that the bats are responsible for the spell, Kenshin is able to break free and defeat both Ren and Baku.