Takahashi Tetsuo, a biology teacher at Shizaki High School, has been fascinated with "demi-humans," beings with characteristics that differ just slightly from humans, since he was in college. He wishes he could have a chance to talk with one, but since the demi-human population is fairly low, he's never even met one. But then the school gains a new math teacher, Satou Sakie... who happens to be a succubus.
It's entirely possible for only 
one twin to be a demi.
.من الممكن تمامًا لتوأم واحد أن يكون ديمي
Es posible que una melliza
sea demi y la otra no.
Es posible que una melliza
sea demi y la otra no.
Non è improbabile che in una coppia di gemelle
solo una sia un Demi.
É plenamente possível que só
 uma irmã gêmea seja demi.
Ничего удивительно, что только
одна из близнецов — деми.