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.
She's the little sis I'm proud of!
!إنّها الأخت الصّغرى الّتي أفخر بها
Ich bin stolz auf
mein Schwesterchen!
Es mi querida hermanita.
Es mi querida hermanita.
Je suis fière de ma petite sœur !
Lei è il mio orgoglio!
A minha caçula é um orgulho!
Она — моя гордость!