Cellular Regeneration
Wood is a mystically or supernaturally imbued material, in a way that plastic and metal are not. Being living or formerly living thing or retains some essential element of natural Earthly life that is inimical to otherwordly energies; an elemental force that plastics or metals do not have. Wood also stores within its cells, through photosynthesis, the same element that sunlight possesses. This technique alchemically breaks the physical physical structure of wood into its most basic form and them imprints it onto the body. As all matter is simply energy expressed in form this technique actually exchanges the energy that forms their body with the energy of wood. The cellular structure of the new body is similar to that of the old, but has more in common with plant tissue. Because of this the body sustains itself through photosynthesis and is capable of absorbing solar energy and storing it. The body stores and processes solar energy at a rapid rate enabling it to regenerate damaged or destroyed tissue with far greater efficiency than an ordinary humans. Just like how the branches cut off a tree will grow back, user is impossible to kill by normal means. Any damage they receive will easily regenerate within a few seconds, be it lost limbs or complete disintegration. To destroy user, every cell in their body has to be destroyed.