After being appointed as the middle boss of Shijima Cave, Ichi Monster Nargoa is dismayed by its uselessness. Determined to revamp the dungeon, Nargoa initiates a massive transformation. Despite facing rejection from brave parties even a year later, the once lackluster cave evolves into a formidable labyrinth. When legendary heroes, having vanquished the Demon King, challenge Nargoa, the monster fights back to protect its loyal employees. In a twist of fate, Nargoa finds itself reincarnated a century later into a world teeming with thrilling boss battles, alongside the employees of the now legendary Shijima Cave turned labyrinth. The stage is set for an epic fantasy adventure to unfold!