yn is a powerfull monster and demon stundent in disguise as human just transfer to the irregular at magic high school and meet tatsuya shiba and his sister , tatsuya see something in yn when yn protect the school and the student when a some stranger try to take control the school , he impressive when yn kill the stranger. after the the try to take control the school tatsuya and his sister go after yn and thank her for safe the student and the school and ask her to be they friends , yn said yes. They became friend from there.