Thirty-five-year-old janitor Akira Tennou is on his way home from work when he is hit by a truck. Instead of dying, he finds himself dragged into a malfunctioning hero-summoning spell and unceremoniously dumped into a gloomy, unfamiliar forest in a parallel world. The forest is shrouded in a sinister black mist, which Akira, drawing on memories of his younger sister's fantasy manga lectures, suspects is an evil curse. His suspicions are confirmed when he encounters an enormous, hostile silver wolf corrupted by the same mist. Instinctively, Akira cries out Purify and discovers he possesses a unique magical power capable of banishing the curse and healing the creature.

As Akira explores his new surroundings, he learns that the forest's residents are all intelligent animals, many of whom are the rightful rulers of the land, driven mad by the centuries-old curse. His purification magic not only restores them to health but also allows him to communicate with them. He begins befriending these creatures, including the silver wolf and other legendary beasts like Fenrir, Dire Wolves, and later dragons. Unlike the traditional heroes summoned to this world who receive gifts that brainwash them and suppress their identities, Akira's accidental arrival and his subconscious control over his abilities allow him to retain his sense of self, though he initially struggles to remember his own name.

Settling into the forest, Akira uses his immense and imaginative magical power to build a home and create intelligent, independent golems to assist him. His primary goal is to systematically cleanse the land and its inhabitants of the curse, a task that has consequences far beyond the forest's borders. His purification efforts inadvertently weaken a powerful magical stone that is the source of the curse. This act also breaks an age-slowing spell on a nearby kingdom's tyrannical king, leading to political upheaval and the rise of a new, better ruler. Akira remains largely oblivious to these world-altering events, more focused on befriending cute, oversized animals and improving his quality of life in the forest.

In later narrative arcs, Akira's power and influence continue to expand. He attempts to venture beyond the forest but is confronted by new threats, including the sudden appearance of an active volcano and a floating island near his home. He also discovers that someone has been manipulating his animal companions through brainwashing, forcing him to investigate the source of this new menace. His actions begin to attract the attention of higher powers, including gods and the errant divine apprentices whose failed experiments and corrupted magic stones are the root cause of the world's problems. By inadvertently purifying and redefining the very nature of magic in the world, Akira thwarts their plans for escape and ascension, and even saves the planet from destruction by replenishing the divine power in its core.

As the story progresses, Akira's power grows to god-like levels, yet he remains a humble, doofy, and all-loving protagonist who is more concerned with protecting his home and fluffy friends than with his own legendary status. His accidental heroism continues to dismantle ancient evils, topple corrupt regimes, and fundamentally reshape the world, all while he remains focused on his simple desire to live a peaceful life petting cute, and often very large, animals. The series follows his ongoing journey as he transforms a cursed wasteland into a sanctuary for legendary beasts and inadvertently ascends to a position of unimaginable power through sheer kindness and a talent for cleaning.