Aki Sora

Sora continues his incestuous relationship with his sister Aki, keeping it a secret from everyone else. Meanwhile, his twin sister Nami forces him to join the Fashion Research club which her friend Kana Sumiya, who has a crush on Sora, is a part of. While Sora looks after Aki, who catches a cold during one of their secret get-togethers, Nami, who is secretly in love with Kana, asks Kana to pretend she is Sora while they practice kissing. This episode incorporates Chapters 2, 3, and 4.5 of the manga. Source: Wiki

Nami persuades Kana to go on a date with Sora, but snaps when she witnesses Kana pleasuring Sora in the classroom while dodging from rain. The next day, Nami tries to confess her love to Kana, but she misinterprets it as about being best friends. Nami turns her anger towards Sora, slapping him to the floor and raping him. The two then reach to have consensual sex, with Nami ignoring Sora the next day on. This episode incorporates Chapters 7, 8, 9, and 15 of the manga. Source: Wiki