Mitrof, the gluttonous and seemingly useless third son of Viscount Vansankai, is abruptly expelled from his noble home at age fifteen. His father, exasperated by Mitrof's excessive eating and lack of ambition, compares him to a "wise troll" and orders him to leave with a Labyrinth Guild pass, expecting him to die there. Though given meager funds by his father, Mitrof receives a heartfelt donation from the household servants, a gesture that underscores his new, harsh reality. He resolves to earn a living in the Labyrinth, his only perceived option, and experiences a profound emotional turning point, weeping over his lost noble life and the daunting uncertainty of his future.
Entering the Labyrinth, Mitrof, armed only with a rapier, quickly finds himself overwhelmed by fear when confronted by a Goblin on the second floor. He is saved by Gracielle, a blue-eyed, long-eared elf hunter who speaks with an old-fashioned cadence. Mitrof reflects on his past: once a talented swordsman, he was beaten by his father for winning a duel against a marquis's heir, leading him to abandon the sword and embrace a life of gluttony and idleness. This past now manifests as a heavy, unfit body. However, after Gracielle's rescue, Mitrof manages to kill a Goblin himself, experiencing a rush of adrenaline and a newfound sense of purpose.
Deciding to return, Mitrof encounters Gracielle again, this time struggling against a dangerous Kobold. Despite Gracielle's pleas for him to flee, Mitrof, asserting that "In the Labyrinth, we help each other," joins the fight. Together, they defeat the Kobold, and both experience "Sublimation," a Labyrinth phenomenon that enhances them. Mitrof discovers not physical strength, but a profound calmness and intuition in combat. Recognizing their compatibility and mutual trust, Gracielle proposes they form a party, which Mitrof accepts, revealing his status as an exiled noble.
As a newly formed party, they register at the Labyrinth Guild, where Mitrof earns his first money, a deeply significant moment for him. Over a celebratory meal, Mitrof's gluttony resurfaces, but he resolves to lose weight to improve his combat effectiveness, a decision Gracielle supports by ordering him more food.
Their next delve takes them to the third floor, where Gracielle's scouting and archery skills prove invaluable against Goblins and wolf-like "Fangs." Mitrof's Sublimation manifests as an extraordinary calmness, allowing him to precisely kill a Fang with a single rapier thrust. They face a pack of Fangs, including a formidable Boss Fang. During a coordinated attack, Mitrof's enhanced mental clarity and Gracielle's quick thinking save him. Mitrof confronts the Boss Fang head-on, impaling it but holding his ground even as it bites his shoulder, driven by his noble training to "never let go of your sword." Gracielle, though impressed, advises him to prioritize practicality over honor and consider his fighting style or weight. They learn about "Gleaners," scavengers who live off abandoned monster corpses, a stark reminder of the Labyrinth's harsh realities.
After narrowly avoiding a larger pack of Boss Fangs, they return to the surface, planning a rest day to acquire better equipment. They discuss pooling their meager funds for shared resources, a practice Gracielle learned from her adventurer father. Mitrof, still battling his appetite, agrees to contribute more for food, solidifying their partnership and shared goals as they embark on their new life as adventurers.
