The story begins with Keita Suminoe, a male third-year junior-high school student studying for his high school entrance exams. He is living in a home with his older twin stepsisters, Ako and Riko, who kiss, flash, and display their love for him in public. They help him prepare for his exams. Keita begins to become romantically attracted to his two stepsisters and he initially dislikes himself for it, though they share no blood-relation to him. Seeing this attraction, his two parents encourage him to eventually get married to one of them, with Ako and Riko constantly at odds to try and get Keita's attention, or working together to keep his attention away from other girls.Source WikipediaBased on the manga Kiss x Sis.