Gisuke Sasaki holds the position of physician at Shōnan Special Reformatory. Under the pretense of medical necessity, he performs invasive and humiliating rectal examinations on newly arrived inmates. He exploits his authority to sexually abuse vulnerable boys, often targeting them with false promises of early release or other incentives. His predatory focus centers significantly on inmates perceived as attractive, such as Jou Yokosuka, prompting protective interventions from other inmates.

Sasaki previously abused inmate Eiichi Hagino, who shared a cell with Rokurouta Sakuragi. Driven by desperation to care for his terminally ill mother, Hagino complied with Sasaki’s demands based on fraudulent promises of early release. Upon discovering the deception, Hagino committed suicide, leaving a detailed note for Sakuragi exposing Sasaki’s actions. This suicide note serves as critical evidence implicating Sasaki in systematic abuse. To prevent exposure, Sasaki conspires with sadistic guard Ishihara to ensure Sakuragi never leaves the reformatory alive.

Publicly, Sasaki maintains a professional façade advocating for humane inmate treatment while privately collaborating with Ishihara. Ishihara delivers boys to Sasaki in exchange for payment, though he later expresses discomfort with their arrangement. Their partnership deteriorates after Ishihara murders sympathetic guard Kumagai to protect their secrets. Sasaki retaliates by physically assaulting Ishihara for this reckless act, fracturing their alliance.

Years after the reformatory events, Sasaki pursues a political career, campaigning for mayor. Former inmates from Cell 6 discover his candidacy and orchestrate his public downfall. They secretly record his confession to past crimes, including abuse and corruption, and broadcast it during a campaign speech. This exposure leads to his immediate disqualification from the election and subsequent imprisonment.