The protagonist, a 34-year-old single male civil servant, finds himself overwhelmed by an immense workload stemming from a recent legal amendment that necessitated a review of document management. This review unearthed a mountain of neglected paperwork from his predecessors, creating a crisis that could lead to severe repercussions for his department. Despite his poor health and exhaustion, he feels compelled to rectify the situation, partly out of self-satisfaction and partly to protect his younger, married colleague, who has a family to support.
While attempting to rest, the protagonist experiences a sudden collapse and awakens to a disembodied, mechanical female voice. He finds himself in a strange, dark, geometric space, unable to see his own body. The voice identifies itself as a "will decision support system" integrated into a "core," which he touches. This initiates a "tutorial" where he learns he has been reborn as a "Dungeon." His objective is to grow and maintain himself by understanding his new form.
He discovers his status includes skills like "Generation," "Storage," "Decomposition," "Analysis," "Appraisal," "Creation," "Enchantment," and "Thought Wave," along with unique skills "Synchronization" and "Incarnation," and a "Goddess's Blessing." He learns that his name is lost, and his core has a durability of 10,000 DP (Dungeon Points), which are used for expansion and creation. He successfully uses "Generation" to create a new room and a connecting passage, consuming DP. He then learns he has been reincarnated into a Dungeon in another world.
For "Incarnation," he attempts to create a human avatar but fails due to insufficient synchronization. He eventually succeeds in creating a Shiba Inu avatar, which he can inhabit. However, this "Incarnation" has a month-long cooldown. He then attempts to "Create" a subordinate, a demon, but fails due to insufficient information. The system reveals his core only holds information about "Slime." He successfully creates a slime, which can speak and calls him "Master." He names the slime "Noah."
The tutorial progresses, and Noah is identified as a "Special Individual" and "Dungeon's Familiar." Noah gains new skills, including "Storage," "Mimicry," "Physical Resistance," and "Pain Nullification." The protagonist learns he can "Enchant" skills. He enchants Noah with "Temperature Sense," "Danger Sense," and "Combat Readiness." He also learns that "naming" a familiar enhances its abilities, and Noah gains "Regeneration" and "Division" skills, becoming significantly stronger. He also creates a "division" of Noah, named "Konoa," who also gains the "Will Unification" skill.
The protagonist, now a Shiba Inu, and his familiars, Noah and Konoa, begin to explore the outside world. They discover the Dungeon is located in a desolate plain with two moons. The protagonist learns to use "Stone Bullet" magic by consuming DP and successfully defeats monsters like a "Grass Snake" and a "Horn Rabbit," which Noah and Konoa "Store." He also learns about "Dimension Power" (DP) and how to acquire it through "Decomposition" and absorbing ambient magical energy.
Over the next seven days, the protagonist and his familiars move the Dungeon multiple times, clearing areas and acquiring new skills and materials. The protagonist struggles with the gruesome aspects of consuming defeated monsters for storage but relies on Noah and Konoa to handle the unpleasant tasks. He also develops a trap system using "Generation" and "Creation" to defend the Dungeon. He learns he can switch between his avatar's perspective and a Dungeon-wide overview.
He discovers the ability to "Enchant" skills onto his familiars, enhancing their abilities. Noah receives "Danger Sense," "Combat Readiness," "Physical Resistance," and "Regeneration," while Konoa receives "Will Unification." The protagonist also learns that "naming" familiars enhances them and that "Will Unification" allows for coordinated actions among multiple Konoas. He also creates a water bath for his familiars, which they greatly enjoy.
The protagonist learns he can relocate the Dungeon entrance by using his avatar as a beacon. He moves the entrance to a new location near a forest. He continues to hunt monsters, acquiring new skills like "Earth Magic," "Earth Resistance," "Scale Hardening," "Soundless," "Endurance Enhancement," "Presence Sense," "Stealth," and "Paralysis Liquid." He also learns that "Earth Magic" requires specific incantations and techniques to activate, which he obtains by analyzing a "Stone Bullet" spell. He can now cast "Stone Bullet" by consuming DP.
The protagonist's DP reserves grow significantly, and his synchronization rate with the core increases. He also discovers a new type of ant, "Syrup Ant," which he hunts for their sweet nectar, despite the painful attacks. He forms a strong bond with Noah and Konoa, who express their loyalty and trust in him. The narrative concludes with the protagonist and his familiars continuing their exploration and growth in this new world.