Choukyou PTA: Tanetsuke Sareru Onna Kyoushi

Mai, a teacher, is being trained into sexual submission by the head of the PTA. What she doesn't know is that he has a strange fetish for abandoning women after impregnating them!
(Source: Coolmic)
Note: Released in long-strip format in 12 episodes, and later sold in traditional format in 4 chapters.