Koma is a perverted demon, a Komainu, that Aoi made a contract with to get more power.
Koma is created by Ryuhei Tamura who has no information regarding any inspiration used to create him. His name is a short version of Komainu. Komainu are lion-dogs that guard Shinto shrines in statue form. He first appears in Beelzebub chapter ? of volume ? and episode 51. His Japanese voice actor is Naoki Tatsuta.
He augments Aoi's sword fighting abilities. Koma can also materialize into a great lion dog.