1) Twins:
Moe-rin (Moeka) attends an all girls school. Shino-chan (Shinobu) attends an all boys school. They're brother and sister twins who are very close, but Tori-chan (Professor Torikai) from the all boys school falls for Moe-rin at first sight, and Shino-chan is hot for Professor Mifuyu of the all girls school. They're still only just kids, but which twin will be first to have a sexual experience...?

2) Please Don't Stop Us [Watashi-tachi wo Tomenaide] :
A girl tries to create one final, ultimate memory for her boyfriend, who has to leave the country because of his father's work.

3) Central Kyoto Love Story [Shijou Riverside Town Love Story] :
The story of a girl who transfers to a Kyoto school and her experience with a temple master's son.

Kyouichi is now divorced from his wife and carrying on a tenuous, homosexual relationship with Imagase. He has even become accustomed to having sex with Imagase every day. However, when Tamaki, a young co-worker with a crush on Kyouichi, appears on the scene, it might be the beginning of the end for Kyouichi and Imagase.
(Source: presencedear)

From Miista MangaFox:

"Sensei, is this a boy or a girl?"
"Do you want to know?"

Ichijo Mashiro and fellow classmates are enlisted in a mysterious weekly class that takes the form of a shared nightmare. Like most teenagers, Mashiro has a secret.. he's neither fully male nor female!

So far, Mashiro's been able to live life as a boy, but all this changes when he's informed of a new class he 'must' partake in order to graduate from his elite preparatory school. To pass, he must find the key and the one way to find it is to enter into a nightmare world, where his body and soul are put at the mercy of the worst kind of enemies -- other school students, who are battling to find the key.

From renowned author Mizushiro Setona, comes a riveting epic mystery that lies between the students, that will have you engrossed from one page to the next. Happiness, sadness, blood and tears will all be shown, but which one leads to an ending? Take the next step into the world of After School Nightmare!