After school, the classroom buzzes with heat, leaving Mio and Karin drenched in sweat and listless. Mio's blouse is soaked, with visible sweat stains under her arms and around her neck. Karin has a fetish for the scent of girls' sweat, especially armpit odor. Tempted by Mio's natural aroma, she secretly sniffs without being noticed. Unable to restrain herself any longer, she confesses her armpit fetish and pleads with Mio to let her smell her underarms.