When Griffith realizes that he will no longer be able to actualize his dream in his debilitated state, he wishes upon his Crimson Behelit as a final resort. Doing so triggers the "Eclipse"—a ritual in which the invoker sacrifices something of significance in exchange for great power. Griffith ultimately chooses to offer his legion of devoted followers, the Band of the Hawk.
Subsequently, Griffith transcends to the Abyss where he faces an enormous entity akin to God. The being introduces itself as the Idea of Evil. Coveted into existence by humanity's collective subconsciousness, it has gone on to manipulate the lives of humans throughout all world events.
As Griffith now exists as a part of the human consciousness, present in the Abyss, the Idea of Evil eerily declares "Your desire is my desire... May your actions bring pain or salvation to mankind. Do as you will, Chosen One." With that, Griffith harvests the pain of his comrades to transform into his ideal self.
[Written by MAL Rewrite]