Yuu’s older sister Maaya is quite popular, being both beautiful and friendly. He is proud of her, and likewise she cherishes him as her little brother. However, after a certain chance happening, her frequent teasings became naughty temptations. Her actions became increasingly bold and he had no choice but to follow along. However, there were no worries about their indecent relationship; instead, it was a enjoyable happy time with his dear onee-chan.