Keita Sato is a 41-year-old single salaryman stuck in a grinding corporate job, burdened with tedious tasks and constant workplace stress. For eighteen years, since a mysterious cataclysm caused labyrinths to appear across modern Japan, Keita has found an unusual outlet: he sneaks into the dungeons that now dot Shinjuku, using them as his personal batting cage. Armed with only a metal bat, he descends into the deepest floors alone and blasts ferocious monsters into submission, treating the whole affair as a simple stress-relief routine.

Keita shares his home with his niece Hikari, a clever and observant young woman. One day she secretly tails him, discovers his secret hobby, and begins livestreaming his dungeon runs without his knowledge. The footage goes viral almost instantly: viewers are stunned by the plain-looking middle-aged man who effortlessly demolishes monsters that top-tier adventurer parties struggle against. Keita remains completely unaware that he has become an internet sensation, while Hikari’s channel explodes in popularity and draws the attention of famous streamers, professional dungeon divers, and even shady figures.

As the story unfolds, Keita’s mundane life and his hidden double life collide. At work, he faces unreasonable demands and harassment—including a manager who pressures a female colleague into sexual favors and a false accusation of groping from a fellow streamer. Each time, his mounting frustration drives him deeper into the dungeon, where he lets loose on monsters with particular thematic vices (such as the “Inmagu,” a dungeon filled with lustful creatures). Meanwhile, Hikari’s broadcasts attract not only fans but also rival streamers and criminals who try to exploit or challenge the mysterious “salaryman hero.” Keita, however, remains blissfully ignorant of his online fame and treats every confrontation as just another bothersome day at the office or another chance to blow off steam.

Narrative arcs include Keita’s accidental rescue of prominent dungeon streamers, his involvement with the shady DOOM Pro organization, a home invasion by violent thugs that forces him to fight in the real world, and his growing web of relationships with Hikari, his coworkers, and the streamer community that orbits his secret identity. Through it all, he never seeks recognition or glory; he simply wants to keep his job, look after his niece, and swing his bat at monsters after a hard day’s work. The manga blends action, comedy, and ecchi elements with a lighthearted take on the “unwitting overpowered protagonist” premise, set in a world where dungeon crawling and live streaming are everyday phenomena.