A former Japanese man who committed evil deeds in his past life was sent to hell and reincarnated as a low-ranking demon. For two thousand years, he endured the brutal hierarchy of the underworld, constantly fighting for survival against higher demons and caught in recurring wars with heaven. Through this relentless struggle, he accumulated unparalleled strength and combat experience. During a clash between gods, he is caught in the crossfire and banished to an entirely different world, finally freed from the torment of hell.

In this new world, he takes the name Kakyu and lives as a traveling merchant, cherishing the peaceful, ordinary life he had always dreamed of. He frequently visits a friendly frontier village named Yorn, where he has built close bonds with the residents. One day, while delivering hunted thunder dragon meat to the village, he discovers that the settlement has been attacked and completely razed. All the villagers he cared for are dead. Among the ruins, he finds a single surviving baby boy named Alus. Overcome with grief and a sense of debt to the people who had shown him kindness, Kakyu vows to honor their memory by raising Alus to become the happiest person in the world.

Kakyu adopts the infant as his son and begins an unconventional and overprotective upbringing. Drawing on the immense power and knowledge he gained during his millennia in hell, he subjects Alus to extraordinary training regimens from a very young age. His methods are far beyond human norms, involving intense physical conditioning, combat drills against formidable monsters, and exposure to dangerous environments. Despite the extreme nature of the training, Kakyu’s motivations are driven by a deep, loving desire to ensure his son can survive any threat and live a joyful, fulfilling life. The story follows their father-son relationship as Alus grows from a helpless infant into a remarkably capable and compassionate young boy, with Kakyu navigating the challenges of parenthood while protecting him from various external threats. The narrative balances lighthearted comedy, heartfelt family moments, and action-packed sequences as Alus steadily develops into a hero of unparalleled potential, all while Kakyu grapples with the irony that his dream of a slow, trouble-free life has become anything but quiet.