"Mushoku Tensei" is built on several major plot twists and long-term narrative threads that are only fully understood over the course of the entire story, as told in the source light novels. The central antagonist is the Man-God, Hitogami, an enigmatic being who appears in Rudeus's dreams. Initially presenting himself as a helpful guide, his true nature is that of a master manipulator. He is a false god who usurped the original Human God and was sealed in the Void World by the first Dragon God. His ultimate goal is self-preservation, and he manipulates events to eliminate anyone who could threaten him, primarily the Dragon God Orsted and his descendants.
A critical turning point occurs when a future, broken version of Rudeus manages to send a message back in time through his diary. This future Rudeus followed the Man-God's advice his entire life, which led to the deaths of his entire family—Roxy and Sylphy were killed, and Eris disappeared fighting for him. This revelation proves that the Man-God's guidance was a long con designed to isolate and control Rudeus. This forces the present-day Rudeus to break his reliance on the Man-God and ally with his former enemy, Orsted, to actively fight against fate.
The series finale in the light novels sees Rudeus successfully ensuring the Man-God's eventual defeat generations later. He does this by aiding Orsted in his preparations and ensuring his own children are strong and prepared for the future. He does not kill the Man-God himself but lays the crucial groundwork for his demise. Rudeus ultimately dies peacefully of old age at 74, surrounded by his loving family, having truly lived a full life without regrets, thus completing his redemptive arc. His soul then meets his past self, the original Japanese man, and finds peace before passing on.