Happiness (oshimi shuzo) manga

Happiness (OSHIMI Shuzo) summary:

Makoto Okazaki is your run of the mill high-schooler, a perfect bullying target and a closet pervert. One Night he decides to return a DVD to a friend of his and ventures out into the night. He notices a person on a nearby rooftop. The person lunges at him before he is able to make sense of this, and bites into his neck, drinking blood. The Attacker stops drinking blood. At this point Makoto notices, that the Attacker is a beautiful Girl. She asks him: "Do you want to die or become like me?" He decides to live...