One day, the protagonist is on his way home from school when he is suddenly abducted by aliens! He is transported to a school inside a spaceship where a biology class is being held. In order to observe the practice of human sexual reproduction, the main character, who was chosen to be observed, as well as a random nearby girl end up having sex in front of the alien students. Then... an abnormality suddenly occurs in the bodies of the aliens...! The students, who were curious about the sexual intercourse of Earthlings they have seen for the first time, band together and immediately 'put into practice' what they observed in class...!! The first time between aliens... Copulation... the first orgasm... and powerful reproductive activities with overwhelming sensual sensations and overwhelming physical disparity... Will the protagonists be able to successfully complete this lesson and return to Earth...?