Pyry

name is pronounced "PIE-ree"
my mischievous but friendly son
i feel very Dear Winter at him so that's why he has a winter name
might be nathan's bio kid
also the whole nathan design change implies that when people die in this universe, if they have, like, strong emotions or something or generally become a "demon" after they die (with demon not necessarily = evil, just maybe "blessed" by the gods to live again), that implies that this kid is.... well.
maybe he was involved in the war. maybe he died and nathan feels like shit about it