Responses
Isn't it because it's human's blood? In the world of demons it should be pretty rare and have strange effects on objets, like the way it summoned the teacher to become a familiar instead of another creature. It's because Iruma is human that the spell changed into a ceremonial invocation of a demon with the seals of the teacher being the base.
True true. But who knows? Foreshadowing
Okay but like, that iruma's blood need to be addressed soon. Cause honey, the theories? His blood plays a major part in it ╮(￣▽￣)╭