the ‘elixir’ is cultivated in the area of the lower tanden, the ‘elixir field’ or ‘cinnabar field,’ also called the kikai tanden, ‘the ocean of ki-energy,’ the center of breathing or center of strength, located slightly below the navel.
This passage provides the most technically complete definition of the elixir field in the corpus, identifying it anatomically, naming its synonyms, and situating it within the broader Taoist internal alchemy tradition from which Hakuin’s somatic practice derives.
, Wild Ivy: The Spiritual Autobiography of Zen Master Hakuin, 1999thesis