So the essence is sex ? Like Skinship or exchanging fluids or smth?

I'm wondering the same. I thought he actually drink his partner blood, but if it is just something like semen or energy coming from sex, that makes everything pretty much simple. Better way to be a half vampire haha

This chapter implies that because he is only half vampire, his body can't handle drinking blood. I wonder if he gets life energy from a specific action during sex, since he said it didn't help this time. So maybe their sex didn't involve enough of something, like kissing on lips or whatever. Or it did work but he's just super tired and overworked.

Yeah ! I just hope it's something different than the usual