An early and powerful antagonist that constantly tries to bring down Shirasagi.
He's a teacher at Shishidou academy, but acts more like a demented prison warden. He deals with the school's "problem children", giving out punishment and using student for his own plans. He lives for the downfall of others and is just as content to see Shirasagi or his own allies fail.
Abidani is the main organizer to the Dice-Challenge arc, and hold's secrets regarding Shirasagi's family.