Souya, a pragmatic and cynical Japanese man, is recruited by a mysterious corporation to retrieve a monster material from the 56th floor of the 'Odori-ji Spire' dungeon in another world within a year. His motivation is to earn money for his sister, Yukikaze's, surgery. After a rushed briefing and a chaotic portal entry, Souya finds himself alone on a grassy plain, his team missing, and his AI companion, Makina, severely damaged.
Souya manages to repair Makina, a cheerful AI with a serious sub-personality named Izola, who reveals the mission's low success probability (0.2%) and the portal's long cooldown (330 days). Souya refuses to abandon the mission. He makes first contact with Gettobad, a friendly fish-man priest who, thanks to 'Babel's Blessing,' speaks Japanese. Gettobad provides local knowledge, including the fact that Souya cannot enter the dungeon without a god contract.
In the Adventurer's City, Souya attempts to register but is denied due to his lack of a divine contract. His stolen supplies lead him to confront the Zava Night Owl Merchant Guild, who are arrogant and dismissive. Souya retaliates by detonating his stolen containers, destroying their warehouse, and threatening the guild's matriarch, Holzard Zava, into submission. He then resolves the issue with the true culprits, the Elomea West Phoenix Merchant Guild, by destroying a magical artifact influencing their young guild master and freeing Gettobad's granddaughter, who had transformed into a human for love.
Souya's desperate need for a god contract leads him to Mislanica, a grey cat who reveals herself to be an ancient "evil god" of deception. Souya pledges himself, and Mislanica, in turn, grants him a contract, allowing him to register as an adventurer. However, Mislanica's divine influence renders his adventurer scroll blank, hindering his ability to lead. Izola pragmatically suggests abandoning Mislanica for a more reputable god, but Souya struggles with the moral implications.
Souya joins a temporary party for his first dungeon dive, led by the veteran adventurer Medim ("Oyaji-san"), who is also Evette's father (Evette is a "Horn," a dungeon monster, not a beast-person, and property of King Remuria). His party includes Arvin, a noble knight seeking to clear his sister's name; Shuna, a young sword-user proving his beast-person master's strength; Bell, a "god medium" with 35 divine contracts; and Zenobia, a magic-user. Their first encounter with 'Chocho' monsters is successful, but their overconfidence leads to a terrifying chase by a giant dungeon pig. Souya, with Bell's plant magic, manages to impale the pig, which Medim then finishes.
Souya, exhausted but with a newfound sense of accomplishment, seeks a bow master. He finds Laua-Lyuna (Rana), an elf he previously helped, who agrees to teach him. Her sister, Air, is injured, and Souya offers them hospitality at his camp, where he continues to grapple with his unique circumstances and the complexities of his new world.
