Please help me T~T

So I'm looking for this manga I read quite some time ago but forgot about it until I read a manga that somewhat reminded me of it but I cant remember the title T~T. It was about a girl and this assasin (or maybe a killer) and apparently she was supposed to be a target but she tried to bite out the neck of her assailant. Afterwards, I think she fainted and when she woke up she saw the man who attacked her who told her that he was going to "raise" (?) her to become a killer/assasin like he was because she showed a certain symptom (her biting out his neck) that can be found in people that make good killers/assasins. Sorry for the vague description and thank you to any who help me look for this T~T