The story begins with Nakamura Takashi, a 20-year-old man of F-rank, being bullied by his former high school acquaintances in a dimly lit dungeon. He is forced to collect magic stones, the remnants of defeated monsters, as part of a mandatory national service. Six months prior, a meteor shower had shattered, showering the Earth with fragments that created spatial distortions, leading to the emergence of dungeons filled with monsters. Firearms became useless within dungeons, and only those with high "stats" and magical abilities could defeat the creatures. Defeated monsters dissolved into magic stones, which were crucial for crafting weapons and armor effective against them. When monsters began to spill out of dungeons and respawn infinitely, governments worldwide revised laws, making dungeon diving and collecting a minimum of seven magic stones per week mandatory for all citizens between 18 and 65, with exceptions for those with specific skills or medical conditions. Failure to meet this quota resulted in imprisonment.
Takashi, with his abysmal stats (Strength 1, Intelligence 1, Endurance 1, Magic Defense 0, Critical Hit 0, Evasion 0, HP 10, MP 0, no magic or skills), is at the bottom of the F-rank. He relies on being a porter for higher-ranked adventurers to fulfill his quota, earning a meager reward of one magic stone per job. With his deadline looming and only six magic stones collected, he desperately needs one more. His current party, composed of one C-rank and five D-rank individuals, are returning from a dungeon and mock him. As they approach the exit, they encounter an Argos, a B-rank monster. Panicked, the party abandons Takashi, pushing him towards the Argos to create a diversion. Facing certain death, Takashi hears a mysterious female voice offering him a chance in exchange for something, and a pillar of white light engulfs the Argos.
He awakens in the quiet dungeon, finding a postcard-sized, durable paper with a magic circle pattern. He also finds the Argos's magic stone. Upon returning to the surface, his former companions mock him, attributing his survival to luck or the monster overlooking him due to his weakness, and threaten him into silence. Takashi then visits the Equilibrium Adjustment Division to submit his magic stone, where he interacts with Mika Sarashina, a kind employee who treats him normally despite his low rank. Back in his messy apartment, Takashi examines the mysterious paper. Touching the magic circle on it triggers a pop-up window asking if he wants to acquire the "Otherworld Transfer" skill. Initially hesitant, he eventually chooses "YES," and is transported to a foreign grassland.
He immediately gains the "Language Conversion" skill and a status window, revealing he is now Level 1. He encounters a silver-haired girl named Aria, an adventurer, who saves him from a slime, the weakest monster in this world. Aria, a Level 10 adventurer, explains the world's system: adventurers belong to guilds, take on quests, gain experience, and level up. She is surprised by Takashi's lack of knowledge and his unusual stats. He learns that monsters drop magic stones, and some drop other items. Takashi, using the Argos's magic stone, registers as an adventurer at the Adventurer's Guild in Rumel City. He receives 500,000 gold for the stone and uses it to buy basic equipment. He discovers that defeating monsters grants experience points, and he gains 100 EXP from a slime, significantly more than Aria's expected 1 EXP. This rapid experience gain, along with the unusual drop rate of items, leads Aria to suspect he has a "cheat" ability.
Takashi and Aria agree to adventure together, with Aria seeing him as a way to level up faster. They take on a quest to hunt Jumping Bunnies. Takashi, despite his low stats, proves to be an anomaly, gaining 300 EXP per Jumping Bunny, which normally yields only 3 EXP. He quickly levels up to Level 4, while Aria expresses disbelief at his rapid progress. They also discover that Jumping Bunnies drop rabbit meat in addition to magic stones. They sell some of the rabbit meat to a butcher and return to the guild to report their quest. Takashi decides to return to his original world for the night, leaving a message and a significant amount of gold for Aria. He successfully transfers back to his apartment, bringing his new equipment and magic stones with him. The next day, back at university, Takashi is confronted by his former acquaintance Yamada, who demands he act as a porter for a dungeon dive. Takashi, now armed with magic stones and a newfound confidence, refuses, much to Yamada's anger. He then uses one of his magic stones to fulfill his quota at the Equilibrium Adjustment Division, surprising the clerk.
