"Yes," Sephiroth whispers. "You have me. All that I am."

Maybe even more so than that moment in the reactor at Nibelheim - this is Sephiroth's absolute point of no return. In their chaotic escape from Nibelheim, Sephiroth had stolen himself, had stolen Shinra's property. Now, to render the theft complete, he has fenced himself to someone else.

He reaches across, now holding Genesis's face between his hands. "Whoever your enemy is, I will destroy it. Whatever blocks your path, I will tear it down."