Cherry & GAL's↑↑

Ruruna feel not confident in her Gyaru association (Gyaru term used for fashionable young girls). Because Ruruna had never had sex, so she could not participate chatting and telling stories with Gyaru friends who are always talking about sex problems. Finally, Ria offers to Ruruna to have sex with Ria's younger brother, so that Ruruna can have experience about sex and can come to tell stories with other friends about sex. (Source: Translated and Edited from Nekopoi)

Younger Sister Juice

Akira's father, an archaeologist, has remarried, giving him a new stepmother and three stepsisters, Yuki, Nana and Miu. While on his honeymoon, Akira's father makes an archaeological find and decides to stay on site in order to supervise and leaving Akira at home alone with his new family members. After being discovered in bed with Yukie, his stepmother, Akira finds a box containing a scroll and three bottles. Using the knowledge his father taught to him, he reads the Sumerian language on the scroll and finds himself in a contract with the goddess Inana, who tells him to collect the love juices of his sisters in the bottles before the next full moon or else a terrible horror will befall him. (Source: Anime News Network)

Gibomai

A renowned painter dies of heart disease while being married with Megumi, a woman much younger than he is. His son, Kyosuke, never liked that union and wants Megumi out of the house. Therefore Megumi proposes that Kyosuke can do anything he wants with her daughter Yuna, Kyosuke's stepsister, if he allows them to stay. Naturally, Kyosuke accepts. (Source: AniDB)

Sex Exchange (1)

Yoshugara Hikaru and his little sister, Mioto, are childhood friends of Sugihara Hakuro, and Hakuro's little sister, Akimi. Although Mioto and Hakuro love each other, Hikaru is also secretly in love with Mioto. One day, Akimi walks into Hikaru’s room whilst he was playing with himself while spying on Mioto and Hakuro. Akimi demands that Hikaru finds a way to break-up their sibling as Akimi also loves her brother. Hikaru refuses her but Akimi threatens to reveal his shameful act. Hikaru loses his temper and rapes her. Horrified by what he had done, Hikaru eventually agrees to cooperate with Akimi on condition that his indiscretions be kept secret. (Source: AnimeNfo)