The fruit is the Golden Flower - the Elixir of Immortality - the Golden Pill. Taoists had many names for it both within internal and external alchemy (though most Taoists believed in internal alchemy - there seemed to be the belief that external alchemy was more philosophical than practical, as evidenced by the fact that most who consumed "elixirs of immortality" promptly died... which fit well with the "no shortcuts" philosophy).
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That is my most recent and most encompassing theory.
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This is where I specifically talk about the Elixir of Life - it's interesting to read over it since it's a relatively old theory and a lot has happened since then. Neat to see where I was on to something and where I appear to have been off base.
Now - if you want in on what's about to happen that people are going to call an "Ass pull" and "fan service:"
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