Based on the adult game by C: drive. 
 
When Mishiro was small, half of his soul was eaten by a toothed deity. Since then he has had to deal with spirits called kotowari that reside in the darkness of the souls of people who are related to him, no matter how distant. Kotowari are soul fragments created from a person’s suffering and they can normally only be seen, heard and touched by that individual. Even if the kotowari is destroyed, it will keep respawning unless the cause of the suffering is resolved. Shortly after transferring to a school in a history-laden sightseeing town, Mishiro encounters a kotowari and decides to search for its owner. However, there isn’t just one kotowari as many other girls harbour their own suffering. 
 
(Source: Visual Novel Database)

Based on the erotic game by Bishop. 
 
Ryuya has an older sister, Miya. He lives a peaceful school life with his friends. But one day, he and his friends accidentally drink a medicine juice. Once you drink it, you'll become sexually sensitive and get excited. The breasts of the girls who drink it will get bigger and they will need to have sex to cool down. Also, to make a vaccine, they will need to get pregnant. Ryuya starts having sex with the girls to cool them down and make a vaccine. 
 
(Source: ErogeShop)

Based on the erotic game by Bishop. 
 
Ryuichi's first sex doesn't go well and he can't get an erection since then. He starts to work at a girl's high school as a janitor but his work attitudes are terrible, so his dismissal is decided. When he is depressed to hear that, he meets Midori. And he gets an erection while talking to her. He can't stand it and rapes her. He has only one month to go so he decides to spend his time at school raping as many girls as possible....

Asa &amp; Natsume are both in love with Hajime Saisho. Instead of fighting over him, they both promised to share him equally. However, both girls have to leave him by the end of the summer. As the summer days go by, they each spend their precious time with Hajime, while the day of their fated departure draws near.
 
(Source: Anime News Network)

Nihikime no Dozeu