He is the leader of a group of demon slaying ninjas called the Crimson Lotus and is the only male of the group. He seeks revenge against the demons for seemingly killing his partner and love interest, Tsukikage, though is reunited with her in the third OVA when he finds her alive but heavily injured.
It's ultimately revealed that the demons they've been slaying were failed experiments by the Black Steel to create human/demon hybrids to take over the Earth. Rekka, along with Haruka, are able to slay the leader and destroy the laboratory, ending the threat.
He has had sex with one girl per video. The girls were Haruka, Kureha, and his main love interest, Tsukikage, in that order.