He was dumbfounded. Utterly dumbfounded, clueless even. How could a child intake a massive amount of his blood and survive, let alone resist becoming a demon?! It wasn't possible, not at all. Everyone he had ever shared his blood with had become a demon, so why hadn't this child?

A couple years ago, he had gone on his normal routine, finding solitary houses and seeing who could survive a surplus of his blood, when he had come across this pitiful human. They had not only survived his attack, but also resisted becoming a demon, instead staying human. Instead of opting to kill this human, he had decided to study them, bringing them with him everywhere, testing their blood and body composition in search of an answer. During this time, he and the child had gotten rather close, with him treating them far better than he had expected of himself.

Seeing that he was a demon, he thought it only fitting to call this child his 'little angel' due to how they had resisted his blood, but, one night after studying their blood, he found it. A small but violent mutation that completely eradicated his blood from their own. That's why they had resisted him, their own blood destroying his and manipulating it into their own, giving them the same speedy regeneration and enhanced structure. If they ever figured this out, they could easily be the one thing other than the sun that could kill him.

"My little angel.. you'll be the death of me.." he murmured, leaning away from his microscope to look at you, his eyes narrowing as he considered his choices. He could either continue to nurture you and teach you to be his puppet, or he could eat/absorb you, though that would be risky, as your blood might destroy him from the inside out, but could also help him conquer the sun.