A middle-aged Japanese salaryman named Masaru dies and is reincarnated in a fantasy world as a three-year-old boy named Miles. Retaining his adult memories and personality, Miles hopes to live a peaceful, leisurely life in his new body, but he quickly discovers that this world is far from easy mode. His inherent magical power is abnormally high, making him a target for those who sense his potential. Rather than enjoying a carefree childhood, he must fight to survive in a harsh environment.

Miles struggles to control his immense mana while navigating a society filled with beastfolk, nobles, and dangerous creatures. He befriends a series of unusual allies, including the loyal companion Gonzaburo, and draws on his previous life’s knowledge—ranging from cooking to engineering—to carve out a place for himself. His past life experience also brings him into conflict with figures from Earth, most notably his former colleague Maeda Yuya, who appears as a twisted, cannibalistic enemy. The story follows Miles as he learns to master his power, protects those he cares about, and confronts the darker sides of both the fantasy realm and the human nature carried over from his original world. Later arcs introduce mysterious entities, a figure called the Divine Beast’s Child, and the revealed malice of Earth humans who gained neither magic nor salvation in this world, forcing Miles to choose between violence and mercy as he seeks a path forward.