The narrative begins with the protagonist, referred to as "Master" or "Master," engaged in a fierce battle within a massive cave. He fights alongside his two party members: Tusca, a beastkin with long black hair and a V-shaped boomerang, and a white-haired, light green-haired girl who wields wind magic. Their current opponent is a colossal, yellow-skinned giant known as a Gigant. Tusca uses her powerful boomerang to sever the Gigant's arm, creating an opening for the protagonist. He activates a defensive barrier, "Rejection Field," and a speed-enhancing skill, "Swift Foot," to close the distance. He then inscribes three ancient runes onto his greatsword, "Greatsword of the Strong," which grant him immense power but are mentally taxing and not part of the original game. With a final strike, "High Power Blade," he bisects the Gigant, which dissolves into light.
The protagonist reflects on his situation, having been thrown into an RPG-like world with game-like rules about a month prior. He struggles with the immense power he wields, which wasn't present in the original game, and the mental strain it causes. He is driven by the desire to end "Dungeon the Choice," a cruel game orchestrated by a powerful entity.
The perspective shifts to Kose, a soon-to-be high school student who feels disillusioned with a world where "abnormal" individuals are commonplace, leading him to question the meaning of life and even wish for humanity's extinction. His nihilistic thoughts are interrupted by a masked man, the "Inviter," who emerges from his ceiling. The Inviter reveals that Kose has been chosen as a participant in a mandatory "live or escape" game, with no rules other than the objective of survival and the promise of immense rewards for success. Kose, despite his initial apprehension and the realization of the danger, feels a flicker of excitement, seeing it as an escape from his mundane reality. He chooses to face the game alone, a decision that seems to please the Inviter. Kose is then transported to a cave, where he receives a "Choice Plate," a system interface that allows him to select a primary class (Warrior or Mage) and a weapon. He chooses Warrior and a dagger, automatically learning the "Swordsmanship" skill and "Life Magic." He also selects "Cleric" as a sub-class for healing, a choice he later deems fortunate.
Kose begins his journey in the dungeon, facing goblins and learning to use his skills. He experiences the fear of taking a life but also the satisfaction of survival. He gains experience, leveling up his Warrior class and acquiring new skills. He also obtains items, including a crude bone club and a crude poison spear. He encounters a waterfall area and then a swarm of Gray Wolves, which he defeats, leveling up again and gaining the ability to choose another sub-class. He selects "Thief," which grants him "Thievery" skills, proving useful for identifying edible plants and disarming traps. He also learns "Wall Walking" from a spider skill card.
His journey continues through various challenges, including a giant spider and a lizardman. He acquires new equipment, such as the "Great Hero's Armor" from a skeleton and the "Ring of the Earth Shield," which allows him to manifest a powerful shield. He also obtains a "Great Sword" after defeating a Great Ogre, a formidable opponent. The game mechanics become clearer as he levels up, gaining new skills and the ability to enhance his TP or MP recovery. He faces difficult choices, such as selecting sub-classes and navigating treacherous paths. He also encounters other participants, including a woman named Yurika who has lost her party members.
The narrative highlights Kose's growing combat prowess and his adaptation to the game's mechanics. He learns to use his skills effectively, including "Steal" to acquire enemy equipment and "Wall Walking" to maneuver. He faces increasingly dangerous monsters, including a Great Ogre and a formidable Grey Ogre, whom he eventually defeats using a combination of skill and strategy, including stealing the Ogre's powerful greatsword. He also learns about the game's "bonus stages" and the importance of strategic choices.
The story also delves into Kose's past, revealing his childhood struggles with being perceived as "abnormal" due to his high sensitivity and unique perspective. He was diagnosed with HSP (Highly Sensitive Person), which his parents initially dismissed as a mental illness. This experience shaped his cynical view of humanity and his feeling of isolation.
As Kose progresses, he encounters more challenging enemies and acquires powerful items, including a "Great Sword" and various skill cards. He also faces moral dilemmas and the constant threat of death. The narrative hints at a larger conspiracy behind the "Dungeon the Choice" game, with unseen observers manipulating events and Kose being a favored participant. The story concludes with Kose facing a powerful boss, the Grey Ogre, and the introduction of a mysterious fairy who offers guidance and hints at the game's deeper mechanics. Kose's journey is marked by constant growth, adaptation, and the struggle for survival in a world that is both a game and a deadly reality.
