The house of Nanami, the older sister, and Yuzuru, the younger brother, was small, so they shared a room and slept side by side in the same room for 10 years. The younger brother was very interested in his big-breasted older sister. One day, while the younger brother was sleeping in the middle of the night, he found his older sister playing with his penis in the futon! From then on, every day the younger brother was treated like a toy by his older sister, giving him handjobs, titjobs, and sex... This strange but natural relationship, in which the younger brother was also satisfied by being made to feel good, continued for 10 years!