Sakamoto, an ordinary college student, becomes friends with a beautiful girl he met at his part-time job, Mari Himeya, through a competitive game, and on holidays they play against each other in his room. One day, however, Mari wore mini-skirted knee-socks. Sakamoto, a big fan of mini-skirts and knee-socks, couldn't help but notice Mari's lower half. As the game heats up, Mari lets her guard down and shows her panties all over the place. Can Sakamoto really hold back his sexual desire for his friend? Of course not!

Note: As a setting, it is treated as a prequel of Isekai AV Satsueitai. The heroine's name may be different, but if you look closely at chapter 4 of Isekai AV Satsueitai, her real name Mari appears at the bottom of her Career Survey.