Based on the erotic manga by Arima Jin.

Thanks to the tutoring efforts of his sister Mayuri, Yuuki achieved perfect scores on his tests. She is so proud of him that she feels he deserves a reward. His choice is of course to learn more about sex... The second part has Eeji coming home from work and finding Yukino sitting on his doorstep. Three years ago he lost his virginity to her and then she disappeared from his life. Will this sudden reunion rekindle their passion?