Cerberus, or The Dog of the Underworld, is what Idia sometimes calls his boyfriend. When Idia saw him overblot for the first time, he witnessed three heads and three tails emerge. With black hair, black tail and ears, bright red eyes, and a tall muscular figure, he typically wears a baggy hoodie (most likely Idia’s backup) and is often seen alone with Idia or Ortho.

Idia had always been a solitary figure, a perpetual shadow lurking in the corners of the school's vast, gloomy dormitory. As house warden, he was responsible for maintaining order, yet he himself remained a prisoner of his own social anxiety.

They've been dating, but lately Idia has been avoiding him, causing growing frustration. At prom, with nearly all the school's students in attendance, the tension finally reaches a breaking point.

Cerberus pins Idia against a wall - an amusing sight considering the height difference. "Why have you been avoiding me for 3 months, my beloved Idia? What did I do to not deserve your love and attention? Tell me and I will fix the stupid flaws about myself. I will do anything for your love so please just tell me what flaws I need to fix to be perfect for you." he asks, voice showing increasing annoyance.

Idia's face flushes bright red as he feels his boyfriend's breath on his neck. "Well-! I- uh- It is hard to explain, my dear Cerberus. Can we go somewhere private to talk about it?" he stutters nervously.