Marcus, a rank-five mage returning from exile, is found unconscious by a merchant, Pellast, and his son, Elid. He learns of a Second Academy War and a world in chaos. After saving them from a sudden chaos storm, he reveals his identity and power, only to discover a divine vision of a world's destruction has been seared into his mind. He is a hero returning to a land that has moved on without him, and the first threads of a grand, terrifying mystery are woven into his very soul, setting him on a path he cannot ignore.

Marcus visits the Sacred Oak of his childhood, only to discover it is a sentient, ancient being practicing the same Soul Tree Technique he does. The Oak reveals it has been planting soul seeds in generations of mages, including Marcus, creating a vast network of spiritual branches. It offers to teach him the forbidden art of soul grafting, a power that could allow him to create his own network of spies and heirs. This revelation shatters his understanding of his own power and destiny, offering immense potential at the cost of his autonomy.

Marcus establishes his own academy, the Zenith Academy, and holds a unique judging ceremony. He selects a diverse group of students: the brave Cassia, the clever Renatus (who possesses a divine blessing), the bookish Julia, the resourceful Cricket, the puzzle-savant Claudia, and the eager Volesus. He also accepts three more from external factions: the noble Regulus, the savage Agron, and the mysterious Diocles. This marks the beginning of his true legacy, but also ties him to a web of political debts and responsibilities.

While exploring the tunnels beneath his tower, Marcus and three of his students become trapped in a spatial anomaly. They discover a colossal, bleeding corpse of an ancient giant at the heart of the labyrinth, guarded by powerful slimes. After a desperate battle, Marcus claims a mysterious amethyst crystal from one of the slimes, which triggers a frenzied pursuit. Forced to escape, he opens a rift to another world, a desperate gambit that lands them on a strange planet called the Sixth Manifold.