Hissatsu Ura Kagyō is an action game set in Japan during the Edo period, inspired by the popular Hissatsu Series historical drama (jidaigeki). The player controls Keijirō Teitō, who by day is a well-liked doctor in his hometown. However, by night, he takes up his sword and exacts bloody vengeance on the wicked and the corrupt.

During the daytime, the player can move about Keijirō's hometown, speaking with people to gather information, visiting the many shops such as a restaurant and a bookstore, and perhaps even getting into a fight now and then. Returning to his home allows him to save the game, view and accept the current job requests, and consult with his father about a variety of topics.

During the night, the game becomes more like a stealth action game such as Tenchu. Controlling either Keijirō or one of several other characters, the player must continue to gather information about the targets for each request while evading detection, eventually reaching the main target who must be killed. Successfully completing requests will earn money and reputation.

Set in the Edo period, Hissatsu Urakagyou follows Kyōjirō Tatewaki, a respected young doctor beloved by the townspeople of Edo. However, beneath his kind and gentle persona lies a deadly secret—he is an assassin of the underworld, delivering justice where the law has failed. By day, he saves lives; by night, he takes them. Under the guidance of his adoptive father, Dōjun, and alongside his fellow assassins, Kyōjirō navigates the dangerous line between healer and executioner. As corruption and crime grip the city, he must face formidable foes, uncover hidden conspiracies, and confront the moral dilemmas of his double life. Will he remain the people’s savior, or will the darkness of his work consume him?