The protagonist of the hentai Ayato Haruno recently confessed his love to his sister Kasumi Haruno - she reciprocated and accepted his feelings. Because the main character's parents went abroad for work, Harumi became not only his tutor, but also his personal "babysitter". According to all the canons of hentai, the idyll couldn't last long. After a while, our protagonist decided to search his favorite porn site while his sister was out somewhere, and what was his surprise when he found a porno with his beloved Kasumi-san...