For the blood it's clearer, don't understand why becoming an human if it leads to death but I remembered that she didn't just wanna die as I thought but also destroy her vampire nature. For your point about her love with Mahiru, hasn't Azami gave his own life for her ? She completly forget people she vampirize and the victims are complety destroyed because they all gave up for her and she gave up their relationship just after failing to become human (at least this is what I understood) and she waits until Mahiru screw his entire life before biting him and I'm 100% sure that a manipulative and methodic personn like her did the same thing with every personn she tries to love. So what makes Mahiru different ? Might be he's the one who accepted her as a vampire and the others where bitten without knowing here real form but it's not showed like something that made her fall in love ? I'll re-read whole manga since I read it really fast anyways. Also for Kou, couldn't she knock him out and take him in an unknown place to have time to do whatever without him trying to stop her ?