Mirin is a 21-year-old college student currently living in a shared apartment with her friend. She has almost no experience using erotic toys, mainly because although they have separate rooms, even small sounds easily carry through the walls—using a vibrator would make its distinct noise and her moans clearly audible to her roommate. Also, since she doesn't have a boyfriend, she's been spending her nights in a state of sexual frustration. For her, masturbating with a vibrator becomes a deeply intriguing experiment. Mirin's first experience with sexual stimulation happened during a tennis club practice. While swinging her racket, a tennis ball accidentally struck her private area beneath her skirt, making her suddenly aware of herself as a woman and conscious of male desire for the first time. Since then, she secretly used tennis balls to stimulate herself during practice. However, living with her parents before college prevented her from buying adult toys, and after moving in with her friend, she's had almost no chance to use a vibrator. Filled with pent-up frustration and wanting to make this summer vacation her final memorable experience, I decided to slowly press the vibrator against Mirin's groin.