Shohei Shindo gains a stepsister, Rino Mizusawa, following his father's remarriage. With her blonde hair, piercings, and miniskirt, she is the quintessential "gal." Shohei, an otaku, and Rino, who speaks in heavy "gal-speak," seemed like two people whose paths would never cross—yet here they are, living under the same roof as family. Rino treats Shohei with friendly ease, unbothered even when he catches her clad in nothing but a bath towel. Shohei, who had imagined a younger sister as someone shy or clingy, finds the prospect of living with a "gal" daunting. However, he discovers that Rino shares his otaku interests, and their communication begins to flow smoothly. Then, one day, a chance occurrence leaves the two of them alone together in the restroom. In that confined space, with their bodies in such close proximity, his stepsister looks incredibly alluring. Drawn in as if by a magnetic force, Shohei presses his lips against hers.