Honestly, I was really happy......when I heard none of us were related at all...!One fateful night, the Shiunji siblings' lives were changed forever when their father revealed they were never really siblings! Now, eldest son Arata finds himself surrounded by cute girls unrelated to him by blood, all of whom have suddenly started acting awfully suggestive. His youngest sister, Kotono, even confessed her love to him! But they're still family, and nothing more...right? Arata's struggle to keep his sisters happy and to suppress his teenage urges has only just begun!