Board Thread:General Discussion/@comment-1875854-20150221232630/@comment-7292165-20150221235700

Crystal = Earth + Water (I'm sure there can be more than one KG with the same elements as the other like Wood Release)

Swift = Wind + Lightning (Wind obviously for incredible speed and lightning too as it can also make you move fast)

Steel = Earth + Fire (Steel is an earthly property. Heat rock to make it hard like steel)

Dark Release I believe isn't a actual nature.