Retsujou Kyoumushitsu

1-4) To Takei, who’s a Math teacher in high school, the school is the perfect feasting ground for students. But never did he expect that one of his former students would become a teacher as well as his colleague! For the number one lusty teacher – Takei, his days of humiliation are starting soon!
(from B-U)

5)Retsujou Kyoumushitsu Extra - Weekends in the Arithmetic Room

6) Our Oath - The mixed up sex lives between a businessman, his secretary, and their two sons.

(Source: M-U)