A virgin is trained for sex by a master of the special move Full-Set Bug Leg Fingers!. He unlocks her hidden desires and preps her for uninhibited lust and group sex. Kyokugen Chikan Tokuiten 3 is a hentai based on the Astronauts: Sirius video game. The story takes place on a crowded train, where the protagonist, Kiichi Kusakabe, silently observes women with provocative attitudes. Rimika Hosho, a popular streamer who performs erotic content, expresses her contempt for sex maniacs during a live broadcast, but ends up crossing paths with Kusakabe. In parallel, Iori Fudo, a college student skeptical about chikan, becomes a victim of one, although she is saved by Kusakabe, who also has a complex history with sex.