I thought Finea mentioned earlier that the spirit kings contract someone every generation, so I thought it would be "all of us" but then I recalled that they're the descendants of the five heroes
and the water thing... no type of water could add a coat to wood. water is water. you can saturate wood in water. a type of deep wood, not the exact name but it's a type of wood that's left to soak at the bottom of a riverbed for years and it triples in weight. it has to be a specific type of wood. thing is, to coat wood, the best natural option is tree resin. *wood already has tree resin? well it still have moisture. "resin" is a type of plastic or hardening agent. wood can soak up lots of it like a sponge. tbh if the fire king already dried them out, flaming them directly gives them a rigidity that basically acts as a hard coat, less effective but a natural method. *but it does turn the wood black