Seine Miyazaki

She is an immortal (316 years old) girl who Tatsuya invites to live in his home; before that she lived in a cardboard box in a park. In the first chapter, Seine looks like a masochist because she likes being bullied. In truth, she becomes close to people who are infected by "mushis" (a kind of parasitic, mind-controlling bugs), in order to hunt them. Her hunting way s go against the kind and pacifist Tatsuya's beliefs. Her motive is to avenge Shimon's (her foster father) death by killing the mermaids from the sea. She controls a black snake like thing called "Aion" that lives inside her. Her weakness is her inability to swim. In the early chapters, Tatsuya calls her "Miyazaki-san". After she moved in, she told him to call her "Seine" because it sounds closer to her real name; means that "Miyazaki" is just made up and she does not really react to it when other people call her that.