Akira Tennou, a thirty-five-year-old janitor, dies after being hit by a truck and is unintentionally dragged into a hero-summoning spell. Instead of arriving at a castle, the failed summoning drops him into a deep, gloomy forest shrouded in a sinister black mist. Drawing on his sister's fantasy manga knowledge, Akira deduces an evil curse is at work. He soon encounters an enormous silver wolf corrupted by the mist. By instinct, Akira cries out "Purify!" and his latent magic banishes the curse, healing the wolf and forging a bond between them.

The wolf, whom Akira later names Shinhi, is the Fenrir king of the cursed forest. The forest's inhabitants are all intelligent, royal-class magical beasts who have suffered under a curse cast two hundred years ago by the human kingdom of Empras. Akira's purification power is not limited to healing wounds; it cleanses corruption, removes curses, purifies land and water, and even generates food and resources. His carefree, positive personality leads him to treat the legendary beasts as ordinary, adorable animals, and he unknowingly earns their loyalty.

Akira decides to settle in the forest, building a home, exploring the land, and continuing to purify its inhabitants and environment. He gains the ability to speak with his animal companions and learns they are the forest's rightful rulers. The story follows his slow, slice-of-life survival as he clears the curse, befriends more creatures—such as the ant queen Shuri, a giant spider, and a pack of mistreated dogs—and reinvents comforts like bread, wine, and bathing.

Unbeknownst to Akira, his frequent surges of mana erode the stranglehold the King of Empras has on the region. The king, growing anxious, sends knight brigades to investigate and subdue the forest. Knight commanders, some of whom begin to question the king's tyranny, find themselves caught in a conflict between a monarch's greed and Akira's unintentional, growing power. Seasonal arcs see Akira contend with summer heat, winter snow, and new threats while his family of purified animals expands. As the curse lifts, the plot builds toward an inevitable confrontation between the peaceful forest and the oppressive kingdom, with Akira remaining blissfully unaware of his own role as the lynchpin of change.