Chosen Undead of Remnant

What happens when the chosen undead, the one meant to reignite the First Flame, is transported to another realm after lighting the flame? How will the members of Team RWBY react to an undead attending their school? And will Y/N be able to end it all? To let himself die? Or will he continue to fight for the citizens of Vale?

I don't own RWBY or Dark Souls