Nakabosu-san Level 99, Saikyou no Bukatachi to Tomo ni Nishuume Totsunyuu!

"This dungeon is completely useless!" One day, a monster named Nargoa is appointed as the middle boss of the Shijima Cave, the very first dungeon located closest to the hero's home base. Upon taking office, Nargoa finds the workplace populated entirely by unconscious employee monsters. Determined to fix this dismal state of affairs, Nargoa initiates a sweeping overhaul of the dungeon. Through tireless effort and major reforms, the Shijima Cave transforms within a single year into a formidable labyrinth capable of turning away even mid-level parties of brave adventurers. However, the situation escalates when legendary heroes, who have already defeated the Demon King, target the dungeon. To protect his cherished employees, Nargoa bravely confronts and defeats these single heroes. Following this extraordinary feat, Nargoa somehow reincarnates into a world one hundred years later. In this new era, a thrilling boss fantasy unfolds alongside the loyal employees from the Shijima Cave, which has now endured through history to become a legendary labyrinth.