Responses
The chapter where Iruma is still new to the school and needed to take a flying test, also where he save sabnoc(big guy who wants to be a demon king) from the giant big bird. He healed the child of the big bird by accidentally dropping a blood from his injured hand.
Iruma found out when his hand was injured and the chick of a big bird's leg was hurt and a drop of his blood dripped unto the wound and healed it. I believed it was during when they had to race somewhere using their wings/summons
Is there part of the story that I missed that says human blood can heal demons? As far as I remember by devouring human it can only make them "stronger". And also it looks like iruma's blood didn't even smell "tempting" to them since they are able to stand there without attacking him.