Hana and Tetsuya were childhood friends who lived nearby for a long time, but when their parents got married, they became brothers. Hana felt lonely because Tetsuya had suddenly built a wall around them after they became family, so she remembered the old days and tried to play doctor and nurse with him, but was surprised to see that Tetsuya's penis was bigger than she expected. Curious, she suggested they play doctor and nurse again and let Tetsuya touch her huge breasts, but... From that day on, she became the outlet for her younger brother's uncontrollable sexual desire...