Board Thread:Theories and Speculation/@comment-1872728-20151008094957/@comment-34334409-20180222072630

I personally like to think that Wood Release is made by one of three things.

1. It's not just the combination of Earth and Water but also has Yang Release and/or Yin-Yang Release added into it. As Yang Chakra is stated to "Breath life into form". Which in my opinion would allow for the creation of plants (which are alive), instead of just getting mud when combining water and earth. Now as for actual wood, Yin-Yang Release is stated by Tobirama to nullify the effects of Ninjutsu. Which could be why it affects Tailed Beasts, as Tailed Beasts and Ninjutsu are created solely from chakra.

2. Hashirama is trained in Senjutsu and found a way to use nature energy without having to absorb it into himself first and is able to add it into his mixture of Earth and Water natured chakra creating Wood Release.

3. The counterpart to the Zero-Tails' Negative/Dark Chakra is drawn to Asura and his incarnations as they are always determined to remain Positive/Light and seals itself or a portion of itself into them. Though this doesn't account for Moegi and other extraterrestrial Otsutsuki Clan members.

The third one is a bit absurd but interesting none the less. Now only Asura, Hashirama, Moegi and a select few Otsutsuki clan members are stated to be able to use is naturally everyone else gained it from Hashirama's cells being implanted into them. Therefore Asura and his incarnation have special Yang chakra. The reason Naruto didn't originally develop the ability is because his original nature affinity is wind, not earth and/or water. Though he did get wood release after receiving the other nature affinities from the Tailed Beasts' and The Sage's chakra.

Once again my opinions and speculations from a wild imagination.