What if theyre just his adoptive parents and Iruma's parents are actually Irumama (this black haired human) and Delkira. Delkira chose to go with Irumama to the human world.
The chapter where Iruma grew a fang after exiting the door can be a hint that he has demon blood in him. I dont think it was Alikred who gave him that bc he just had exhausted his energy trying to maintain the door.

its giving me the impression that henri loves the human girl but never got together??? she might be iruma's tru mom but that may be tio farfetched idk.. it could also be the reason why ameri likes iruma is because henri used to like a human being. it runs in their blood. ORRR ameri's mom died after giving birth to ameri (just a theory)