7 Short Stories About Sex (spanning across 11 chapters):

1-3. 7 Daime no Tomari (The Seventh Generation, Tomari)
Tomari is a cursed woman who must do specific sexual things with her partner or the curse will kill her. Her partner, randomly chosen by the curse, is a guy called Naoki. He's pretty much willing to do whatever she needs, but Tomari will have to get past his incestuous sister Kyoko first.

4-6. Hajimete to,
A teenage couple, Seriko and her boyfriend Ogihiko, find themselves caught in a plot from her crazy yakuza family to make them lose their virginity together.

7. Sandy Go Home
   Yoko returns from studying abroad in America with her sex-crazed roommate Sandy, and they both proceed to fight over who gets to have sex with her brother.

8. Mete Yunde
   After their parents died in a traffic accident, Morote's two older sisters became insane. Is he safe in the house with them any longer?

9. Pastel Ivory
   School kids have a sexual encounter in a bathroom.

10. Ninjia Shoujo Makari Tooru
    When a ninja invades a girl's bedroom, he finds himself completely outmatched by her skills, both ninja and erotic.

11. 80D
    A couple has a sexual exploit in a library after hours.