After dying in a traffic accident while trying to save a falling vending machine, a man who was deeply passionate about these machines awakens to find himself reincarnated in a fantasy world. To his shock, he has been reborn not as a hero or a monster, but as a fully functional, sentient vending machine. He lands near a lake in the wilderness, completely immobile and unable to speak anything beyond the pre-programmed phrases typical of Japanese vending machines, such as welcome or please come again.

The protagonist, who adopts the name Boxxo given by his first companion, quickly learns the rules of his strange new existence. He requires coins inserted into his coin slot to generate points, which are necessary to sustain his life force, power a defensive barrier, and restock his internal inventory. He can dispense any product he ever purchased from a vending machine in his past life, ranging from canned coffee and bottled tea to instant ramen and snacks. As he levels up, he gains the ability to transform into different types of vending machines, including rare or historical models, though this form is limited to a short duration each day. A significant limitation is that people in this world cannot read Japanese, making the labels and instructions on his products difficult to understand at first.

Boxxo's fortunes change dramatically when he encounters Lammis, a young hunter blessed with the Blessing of Might, which grants her superhuman strength that is usually difficult to control. Fascinated by the unusual machine and its goods, Lammis easily lifts the 500-kilogram Boxxo and carries him on her back. This arrangement proves mutually beneficial: Lammis gains mobility for Boxxo and a reliable source of food, drinks, and supplies, while Boxxo finds that his weight helps Lammis stabilize her immense strength. She brings him to the village of Clearflow Lake, where he becomes an indispensable part of the community, selling modern conveniences that astonish the locals. Through a simple system where specific phrases mean yes or no, Lammis develops a unique form of communication with Boxxo, understanding his intentions and conveying them to others.

The story takes place primarily within and around a vast, monster-infested dungeon that adventurers explore for treasure and glory. This fantasy world operates on game-like mechanics, with adventurers belonging to guilds and taking on quests. The dungeon is divided into multiple strata, each with unique environmental hazards, such as intense heatwaves in the Scorching Sand Stratum or the dangers of the Dead's Lament Stratum. The narrative follows Boxxo and Lammis as they navigate this dangerous environment, facing various creatures like King Frog fiends, Flame Skeletitans, and other monsters.

As the series progresses, the pair joins a colorful adventuring party known as the Menagerie of Fools. The party is led by Kerioyl, a rough and skilled fighter, alongside his calm and perceptive vice-captain, Firmina, a powerful magician. Other members include Shui, an archer with a hearty appetite, the reconnaissance twins Aka and Shiro, and the mysterious Michelle. They are supported by Hulemy, a magical item researcher and Lammis's childhood friend, who becomes fascinated with Boxxo's internal mechanisms. Notable narrative arcs include Boxxo being kidnapped by bandits who attempt to extract his money, forcing Lammis and the party to rescue him. Another significant arc involves a search for a missing party member in the Scorching Sand Stratum, where the group uncovers the tragic backstory of a fellow adventurer seeking revenge for a murdered friend. The series blends comedy with moments of genuine tension and resourceful problem-solving, as Boxxo uses his unique abilities, such as combining cola and mentos to create projectile attacks or providing life-saving oxygen in sealed environments, to help his companions survive their dungeon explorations.