Board Thread:Theories and Speculation/@comment-39350828-20200424153111/@comment-39350828-20200428152620

Ninja Of War wrote: Kinda similar to Kimimaro's Shikotsumyaku, that creates osteoblast and osteoclast cells, Hashirama's WR creates WR cells. It seems to not be chakra that has the properties of wood, but rather using chakra to create WR cells.

Therefore, fundamentally different from most ninjutsu. Shikotsumyaku seems to just grow bones from nothing like regeneration abilities. It doesn't turn existing physical matter into bones as far as we've seen. Otherwise he would need to eat a ton of stuff every time he uses it.