The Archmage Awakens (The Sundering Cycle Book 1)

He died saving the world. He woke in chains. When demonic rifts tore the sky apart, he sacrificed everything to save humanity, anchoring his soul to the world's dying mana network as a living shield against the Void. He woke five hundred years later, starved, shackled, and enslaved in the body of a dying boy. This is his journey.