An assistant of Enma Ai who appears to be a handsome young man with one eye covered by hair. He can manifest a single, very large eye that can be directed anywhere, allowing him to see through walls. This manifests as an eye on a wall. The large eye can also be used as a weapon, by projecting intense flashes of light. When so required, Ichimoku Ren becomes a blue straw doll by kissing a pendant he wears around his neck. He is sometimes referred to as "Moku" or "Ichimoto Ren."
It is later revealed that Ichimoku Ren is a tsukumogami, an artifact which has gained sentience after a long time of existence. In Ren's case, he was once a katana, forced to be aware and watch whatever was done with him. He was given his current form(s) by Ai, who collected him after he was abandoned on a battlefield. Ai claims she came to find him because there is something that Ren is looking for, a fact perhaps manifested in Ichimoku Ren's occasional puzzlement and inability to understand the things humans do. Ren has apparently developed feeling for his colleagues, seeing them as family.