Katsuhiko, a young unemployed man, resides in a gloomy apartment. His leisure revolves around navigating subway stations to sexually harass female passengers. He scouts crowded trains for women to grope, cultivating specialized techniques honed by exceptional manual dexterity. This skill allows him to manipulate women's bodies, inducing intense physical reactions that often culminate in climax during the assaults. The same dexterity enables him to win frequently at game arcades, representing his sole income source. He targets women perceived as unlikely to resist or report, whether due to shyness, embarrassment, or unexpected willingness. This reflects his understanding of behavioral vulnerabilities in crowded spaces. He derives deep satisfaction from controlling his victims, viewing their public orgasms as personal victories. Despite his predatory acts, he harbors contempt for perpetrators who use physical violence, distinguishing his methods from more aggressive sexual assaults. His activities draw the attention of Gin, an older man who observes Katsuhiko's technique during a groping incident. Gin recruits him into an organized group of experienced gropers who conduct collaborative assaults on trains, providing mutual coverage. This shifts Katsuhiko from solo acts to coordinated group operations. Under Gin's influence, Katsuhiko escalates beyond groping to include full sexual encounters within the train environment. A recurring dynamic exists with Sayaka, a female investigator who previously experienced his assaults firsthand and now actively pursues his apprehension during train activities. This creates ongoing evasion as he continues his harassment pattern. The central narrative involves Gin assigning Katsuhiko to target a specific high-profile victim: a television anchorwoman. This assignment leads to Gin ultimately betraying Katsuhiko, forcing him to navigate the consequences of this double-cross. His character design features consistent black hair and red eyes, though his exact age remains unspecified.