Ajin, also known as demi-humans or simply Demi, have lived alongside humans for ages under persecution. However, in recent years, they have become accepted as regular members of society.

Takahashi Tetsuo is a biology teacher who has been always interested in demi-humans but never had a chance to meet them. However, in his fourth year of working at Shibasaki High School he starts teaching Takanashi Hikari, a highly-energetic vampire and lover of tomato juice; Machi Kyouko, a shy dullahan who has trouble socializing; and Kusakabe Yuki, a yukionna who avoids people because she is afraid that she might hurt others with her powers. Moreover, the school employs math teacher Satou Sakie, a succubus who constantly suppresses her seductive ability and has zero experience with men.

As Takahashi interacts with demi-humans, he learns more interesting facts about them and helps them solve their problems.

— written by Singan