The kidneys, manifesting the water principle, are the major yin organ; they are located in the lower body. Contained within the five internal organs are seven marvelous powers, with the spleen and kidneys having two each.
In Taoist-inflected Chinese medical cosmology transmitted through Hakuin, the kidneys embody the water principle as the supreme yin organ and are assigned a double share of the body's marvelous powers.
, Wild Ivy: The Spiritual Autobiography of Zen Master Hakuin, 1999thesis