Siblings Sora and Aki Aoi realize they have a sexual attraction and begin a secret relationship. Meanwhile, Sora's twin sister Nami is having trouble dealing with her feelings for her friend, Kana Sumiya, who has a crush on Sora. Sora also meets Runa Satsuki, who seeks thrills doing naughty things in public places.

It is revealed that the Aoi family's mother is actually her twin sister, their real mother having died in a road accident, with Aki being the only one who knows the truth. Runa takes Sora to an orgy where she loses her virginity. Meanwhile, Nami snaps when she witnesses Kana pleasuring Sora, becoming jealous of Sora's "thing" and raping him.