Succubi are demi-humans that arouse sexual desire in men and cause them to have obscene dreams. One such succubus, Satou Sakie, is extremely careful in every facet of her life, from where she lives to the trains she rides to the clothes she wears, so as to avoid causing these reactions in men. With girlish dreams such as romance and marriage so far out of reach, she thought she'd reached a compromise in her own life, but something changes when an accident causes her to grab Takahashi Tetsuo's hand...
The story takes place in an age where "Ajin" (demi-human), more casually known as "Demi," have slowly started to become accepted into human society. Tetsuo Takahashi is a biology teacher who ends up teaching three such Demi, hoping to understand more about them while also managing to catch their attention.
