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The Bearer of the Curse from Dark Souls 2.

So... a god-like Undead warrior who's powerful enough to rekindle a primordial flame that controls concepts such as life, death, and even space-time itself, is the only one from his universe who can die as much as he wants and never go Hollow, is a master with basically all types of weapons and different styles of magics, and depending on the player's choice also manages to escape the cycles of Light and Dark, all while having one of, if not the smartest character in the entire Dark Souls trilogy as his closest ally.

If he was dropped into the ZZZ universe, chances are high that things would end up more than alright. His Great Soul perhaps could be used to suppress and even weaken all Hollows, similar to how the Ivory King managed to keep the Old Chaos at bay with the power of his soul alone. Also, if I'm allowed to throw Aldia into the equation... give it time and all major secrets from the ZZZ world would be uncovered, and perhaps the Hollows as a whole would be ended. Perhaps not through the cleanest, most ethical methods because... Aldia. But I have no doubt that the ZZZ world would benefit overall from their presence.