"I believe Kingdom Hearts... is light!" But seriously, I would not be surprised if...
Derplander is the Warrior of Darkness. I mean, he also has the Echo, and those gifted by the Echo are immortal. You learn this through the Leviathan update especially. To say that Echo-gifted adventurers, like the Warrior of Light, are Hydealynian Ascians would be pretty spot on. And the Ascians gaining their power through some manner of blessing similar to the Blessing of Light would also not be all that much of a stretch. It would explain why, when we had it before meeting Midgardsormr, the Ascians couldn't breach the Scion HQs. Opposites attract, like repel and all that. So the only real quest here is, did Derplander travel the same path we did after Ishgard? This answer would be far more telling than any other.
Append: School fail... it's been a while.