Gisuke Sasaki holds the position of physician at Shōnan Special Reformatory, outwardly championing humane treatment for inmates while covertly orchestrating systemic sexual exploitation of boys in his custody. He allies with the brutal guard Ishihara, bribing him to supply vulnerable or appealing targets—such as the young inmate Jou Yokosuka—for abuse. His predation includes psychological manipulation and physical violation, as seen in his coercion of Hagino, Rokurouta Sakuragi’s former cellmate, whose subsequent suicide he engineers.

Sasaki falsifies medical records to obscure inmate deaths, exploiting his dual authority as coroner to erase traces of institutional violence. Viewing Rokurouta as a threat after Hagino’s suicide note implicates him, Sasaki conspires with Ishihara to eliminate the inmate. This culminates in Rokurouta’s fatal shooting by American soldiers during a staged confrontation.

Despite temporarily evading accountability, Sasaki’s crimes unravel during a public press conference, leading to his arrest. Imprisoned as a convicted pedophile, he faces heightened danger from fellow inmates inclined toward vigilante justice. The narrative concludes without detailing his fate, implying inevitable retribution within the penal system.

Consistently portrayed as a calculating antagonist, Sasaki prioritizes self-preservation without remorse. His backstory remains unexplored, with emphasis placed on his predatory actions and their role in driving the protagonists’ conflicts. His documented appearances are confined to primary manga and anime adaptations, with no expansion into supplementary media.