A hardcore gamer known only by his player name Zephyrus has invested over 8,000 hours into the legendary dungeon-crawling RPG Dungeon Shukatsu no Susume, a game so vast it boasts more than a thousand unique classes and hundreds of possible endings. After suffering the ultimate tragedy of having his save data suddenly erased, the shock proves fatal. However, instead of oblivion, he awakens to find himself standing in the Village of the Beginning Without a Name, the very starting location of the game world he knew so well. Reincarnated into the unconquered realm of Dan-Katsu, he is overjoyed to realize he can now experience his favorite game as a reality. Armed with encyclopedic knowledge of its systems, secrets, and challenges, he immediately sets out to begin what he considers a New Game Plus. Zephyrus enrolls at the Labyrinth Academy, the central hub where the main story of Dan-Katsu unfolds. He quickly secures the classic and most powerful Hero class. However, he soon discovers that the world he now inhabits plays by slightly different rules than the game he remembers. What he knew as the Muscle Warrior, a class considered a joke or purely for fun by players in his original world, is perceived as a genuinely respectable and effective path by the inhabitants of this reality. Similarly, dungeons that he had conquered countless times on his screen remain unbeaten, their deepest floors untouched by any adventurer in this living, breathing world.

Determined to fully enjoy this second life and show the true potential of various classes, Zephyrus begins to reshape the story around him. He uses his foresight to gather a powerful and diverse party, personally guiding his reserved childhood friend into becoming a legendary Alchemist and transforming a haughty, selfish princess into a peerless Saint. By assembling these powerful classes, he sets out to do what no one in this world has ever accomplished: fully conquer the most difficult dungeons. What follows is a tale of adventure and discovery as Zephyrus leverages his veteran gaming expertise to live out his ultimate fantasy, tackling every challenge with the carefree joy of a player who knows all the cheat codes, treating the entire world as his personal playground.