can someone explain what the white hair guy wants? and who was the man at the end

He basically wants to go back to the mountain of fire which was his original home

not the devil

i dont know who the white haired guy your talking about is if not demon, but the guy at the end is someone who has "mastered the fire". They made him out in earlier chapters to be someone who would help build a powerful weapon. So basically hes gonna help make the weapons, alos the prince from Wu country hates him for some reason