The protagonist, Josiah, is a reincarnated salaryman from Japan who finds himself in a world with magic and monsters. Born into a rural village with parents who indulged his every whim, Josiah felt stifled by their passive attitudes and the villagers' complacency. Upon reaching fifteen, his latent magic and profession were unlocked: he became a "Magician" with the rare "Light" attribute. This proved problematic, as Light magic is typically associated with healing and support, and male Light mages are exceptionally uncommon, leading to his enrollment in a school where he was the sole male student among predominantly female students and faculty.
Josiah's primary goal is to master the offensive Light magic spell "Holy," which requires reaching level 10 in Light magic, a feat estimated to take fifty years. He theorizes that by utilizing magic circles, which he views as programmable formulas, he can accelerate his experience gain. After graduating early from his specialized school, he moved to the capital of the A Empire.
Two years later, Josiah's Light magic is stuck at level 9, and he faces potential expulsion from the Adventurer's Guild for his inability to undertake solo dungeon raids. He currently performs menial tasks and temporary support for other parties. To gain experience, he takes on hazardous jobs like sewer cleaning, where he uses his magic circles to purify waste and recover cursed weapons, earning him no monetary reward but valuable experience. He negotiates with the company president to expand his cleaning area, increasing his experience gain. He also provides magical transport equipment to a construction site for a new city wall, offering to supply more than requested to maximize his experience.
Josiah also volunteers at a hospital, using his enhanced healing and repair magic to treat the poor who cannot afford proper medical care. However, his efforts have improved the local health and sanitation so much that there are no longer enough patients to provide him with sufficient experience. He realizes his experience-gathering opportunities are dwindling. His Light magic, while lacking offensive variety, grants him a vast mana pool, further replenished by potions and an intravenous drip during sleep.
Just as he considers leaving the A Empire, which he finds to be a lawless and exploitative place, his Light magic reaches level 10, and he finally acquires "Holy." He immediately begins researching and developing offensive spells based on "Holy," such as "Holy Ball" and "Holy Slash," and practices in low-rank dungeons. He discovers that his "Holy" magic is abnormally powerful, capable of obliterating monsters with minimal mana cost, but this also prevents him from collecting monster parts, which are crucial for guild achievements. He eventually adjusts his technique to leave remains, allowing him to level up his profession and gain guild recognition.
However, the A Empire begins implementing cost-saving measures through "Magic Tools," automated machines that replace manual labor. Josiah finds himself jobless as his previous side-hustles become obsolete. The guild also undergoes a purge, expelling adventurers who haven't achieved sufficient merit. Forced to pay a hefty sum to leave the empire, Josiah travels to W Country, a developing nation adjacent to the E Kingdom, known for its recent dungeon emergence.
W Country proves to be a surprisingly welcoming and well-supported nation for adventurers, offering free lodging, food, and equipment. However, Josiah is suspicious of this unusual generosity. He learns that solo dungeon expeditions are prohibited, requiring a minimum party of four. He is assigned to a party led by Christoph Le Clerc, the son of a prominent merchant, and other noble-born adventurers, whose quest to defeat low-rank monsters is deemed B-rank due to perceived threats from higher-ranked monsters. Josiah finds this assessment absurd and believes it reflects a noble-centric system. He decides to continue his side-hustle of repairing buildings and facilities, which he discovered is not explicitly forbidden, to further hone his magic and earn money.
Meanwhile, back in the A Empire, the introduction of Magic Tools leads to significant problems. The magic-powered gondolas at the construction site malfunction repeatedly, causing delays and frustration. The postal service also struggles with the slow sorting speed of Magic Tools, leading to delivery backlogs and the forced involvement of former adventurers. The medical services, having lost Josiah's free aid, are struggling with severe cases, and the sewer cleaning company regrets firing him. The A Empire's guild, now under stricter government oversight, faces a dungeon investigation request from C Duchy, which relies on the empire's skilled adventurers for its high-difficulty dungeons. A newly formed party, led by a young "Hero," is criticized by a government inspector for lacking support personnel, highlighting the empire's disregard for traditional roles and its focus on individual strength, ultimately leading the Hero to realize the nation's decline.
