Cerberus is legendary hell spawn, summoned by Masato to wreck havoc of a most unusual kind.
It has three heads and three tails.
It are black and brown Dog Demon.
When Annette used a seal to preclude Masato from leaving her house, for having cursed her orb, he summoned it to wreck havoc at her house, by vomiting and urinating creepy animals (snakes, frogs, scorpions, spiders…), much to her disgust. When it eats money from Rinne, he would knock him and Masato out.