no but srsly what the hell is mc there's no way he's a normal human. is he some kind of hy...

Isn't he a vampire hybrid or smth?

My theory is the use is the result of an experiment. The government or that one secret branch wanted to create super soldiers and they were experimenting on orphans. That is why they asked Gun to keep an eye on the new breeds of monsters. And because the uke has monster DNA, he has a connection with them and they can communicate with him. That monster clearly knew the uke needed blood and was trying to provide it.