How is Lord DeRosso immortal?

Question

If you explore Vampire Castle, you'll ultimately learn that Lord DeRosso gained his immortality while burning in his own castle's flames - when some dark voice offered him power everlasting.

During the final battle, Lord DeRosso makes an appearance: before sacrificing himself against Lord Ouroboros, he recites the same words as the dark voice - then he fuses with Ouroboros' core.

But, this still doesn't quite explain Lord DeRosso's immortality - nor is it very clear why did he recite those words (obviously he's the dark voice his past self heard, but I still don't see the point).

So, what exactly makes Lord DeRosso immortal?

Answer 1

I actually don't recall directly either; and I'm not sure it was ever clearly explained. It's an interesting chain of events I can't get straight in my head:

• DeRosso becomes immortal when he sets his home ablaze and hears the voice
• The voice is actually DeRosso speaking during the final battle (beginning the bootstrap paradox)
• During the battle with Sage (1800 years prior to the story's events); he's given a task by the angel only he can complete due to being an immortal

So I guess he somehow was able to make himself immortal?

I'm pulling this from the final fantasy wiki:

Forced to watch the innocents trapped in his manor suffer a lingering death by starvation, DeRosso set his home on fire with the intent to go down with it. Just as he was about to die, beginning to come to the realization that his persecution is unwarranted and that those responsible must pay, DeRosso heard a voice call out to him: "Accept me and I shall grant life everlasting. Though it shall be filled with grief, thou shalt have all eternity to wreak vengeance upon thine enemies". While the voice's identity was unknown to him at the time, DeRosso became an immortal and left the ruins of his home. Demonized as a vampire by the Orthodoxy, deciding to make use their propaganda by giving himself the look, DeRosso gathered many followers who shared his malice towards the Orthodoxy.

In the final world, with Ouroboros's arrival into his reality, DeRosso carries out his promise to the angel by merging into the monster's core. Using his own immortality to negate Ouroboros's regeneration, DeRosso dies with the monster when he is finally destroyed. But prior to his sacrifice, as the Infernal Realm transcends time and space, DeRosso begins a bootstrap paradox by saying the very words he heard long ago so that a past version of himself would hear it.