Tien's father remarried Aunt Hai, so Tien has an adorable younger sister named Ono Rikka. The only problem is that Ono is still a mischievous schoolgirl, and she always shows affectionate gestures towards her older brother Tien. Especially, Ono still dresses lightly, flaunting her smooth buttocks whenever she's at home. After their parents' wedding, they went on a honeymoon, so Ono and Tien had to stay home for 3 days. Because Ono is too innocent and silly, Tien has to order food from a restaurant every day since no one is there to cook. However, while Tien was 'washing the dishes,' Ono discovered this. Will the little girl 'get intimate' with Tien? How will Tien handle this situation?