Ichatsuki Taino

Yugao's grandfather privately owned library stands on a precipice. In this library there is a special room which filled with occult-related books. It is rumored that the room is cursed. Kiryu, a serious man, works alone in this mysterious room. He is crazy about giving lessons to people. Yugao is very fond of him, so she one day she kissed him and he becomes a different person in his attitudes about sex.

(Source: Shoujo Manga Maniac)