After sacrificing his life to defeat the demonic dragon that threatened the world, the legendary level 99 thief Might is given a second chance. A goddess appears before him, offering resurrection and a single wish in reward for saving the realm. Might, who was born without any mana and could never use magic, seizes this opportunity to fulfill his lifelong dream. He asks to be reborn as a Sage, the most powerful magic-using class.

His wish is granted, but there is a cost. Changing classes resets his level from 99 all the way back to 1. He awakens in the body of a fifteen-year-old in the First Town, a bustling entertainment city where he grew up, but he retains all the knowledge, skills, and overwhelming strength from his previous life. Though his displayed level is that of a novice, his actual combat power remains that of a hero who has already saved the world.

Registering at the beginner’s guild as a new adventurer, Might almost immediately encounters a party of three troubled female adventurers. There is Lisティ, a blue-haired swordswoman with a poorly hidden secret; Platina, who claims to be a paladin but has a concealed true profession; and Nanase, an awkward mage more interested in brewing experimental potions than following recipes. Their party is skilled but dysfunctional, and they quickly become attached to Might after witnessing his inexplicable power and knowledge. Due to his new Sage abilities, Might can see mystical locks on people that seal their true potential. By performing an action like kissing their hand, he can perform a temporary unlocking of their hidden techniques, which also accelerates their affection for him.

Notable narrative arcs begin with Might forming a new party with the three girls, naming it the Moonlight Corps, and taking on their first quest. They are sent to a rural village where the crops have mutated into monsters. The party discovers the cause is an earth spirit angered by neglected rituals. To resolve the crisis, they must perform a ceremonial dance in revealing clothing to appease the spirit and eventually enter a dungeon to confront a powerful Earth Golem. At the golem's core, they find not the spirit but a bound earth goddess named Ursula, whom Might frees, earning her devotion. Subsequent storylines involve a mission in the capital city against a nest of vampires, where Might is reunited with former comrades from his level-99 party, such as the sword fighter Faleena. Throughout these adventures, Might aims to master his new Sage class, earn a proper living as an adventurer, and guide his new friends toward their full potential while navigating the complications of his old life catching up with his new one.