A hardworking salaryman in his forties, whose weekends were once consumed by the tabletop roleplaying game Dungeons & Braves, suddenly finds his life cut short. He is granted a second existence as Geo Margilus, the max-level wizard he spent seven years building and perfecting within the game. Transported to the fantasy realm of Sedia, he retains every spell, piece of enchanted equipment, and reservoir of knowledge his character possessed. Level thirty-six and armed with a wizardry staff, Geo quickly discovers that the world of Sedia is a grim place where ravenous daemons known as the Dark Ones (ankī) relentlessly threaten human civilization. The magic system of this world, based on a different principle of sorcery called magecraft, cannot compare to the sheer power and versatility of the dungeon-crawling magic Geo now wields.

Geo's journey begins when he rescues a merchant's earnest young daughter, Mora, from bandits who had taken refuge in a ruined castle. This act brings him into contact with the haughty but capable mage Clora Andel, a noblewoman and fifth seat of the mage guild in the city of Lerys, and the veteran ranger Sedam. Over time, Geo assembles a growing circle of allies. Clora becomes his court mage, Mora becomes his castle's head maid, and her merchant father Ild becomes his steward. He also frees a dark elf rogue named Leiha from a curse placed by daemon worshipers, earning her absolute loyalty, and later gains the tacit support of Ledo, a towering warrior chief known as the Daemon Hunter.

Geo sets his sights on eradicating the Dark Ones. After a series of battles that showcase the overwhelming gap between his TRPG-bred magic and the local magecraft, he destroys a major daemon nest. As a reward, the knightly order grants him a neglected fortress, which he renames Castle Geteius and establishes as his base of operations. With his reputation as a Great Wizard growing, a new threat emerges: a clandestine cult of daemon worshipers called the Demonists begins to stir, plotting against the fragile peace he has started to build. The narrative follows Geo's efforts to defend his newfound home, manage the politics of a medieval fantasy world with the cautious, middle-aged mindset of a former salaryman, and ultimately decide whether to simply survive or to take on the mantle of a true hero fighting for humanity.