Age
316
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.
AiON
Tatsuya Tsugawa has just lost both of his parents in a car accident. While trying to live up to his father's dying wish of becoming an upstanding man, Tatsuya rushes to help Seine--his bizarre classmate--from bullies. Little does he know he is about to find himself in the middle of a supernatural war between the immortal Seine and sea creatures that can control humans. So much for being Mr. Nice Guy!
