The fifth element is the one that most often gets flattened into a single idea across traditions that mean different things by it, so the distinctions are worth stating plainly.
Aristotle's aether is a physical proposal, not a spiritual one. The four elements move in straight lines and are corruptible; the heavens visibly move in circles and do not appear to change; therefore, he argues, the heavens must be made of a fifth substance with circular motion natural to it. That is a piece of natural philosophy answering an observational problem, and the later Latin name quinta essentia, fifth essence, is a translation of that argument rather than a mystical term.
The alchemists took the word and turned it into something else: the quintessence became the extracted active principle of a substance, the thing left when everything inessential had been driven off. That usage is the ancestor of the ordinary English sense of the word and of the practice of distilling essences.
The ceremonial tradition added spirit as a fifth point on the pentagram, above and governing the four, with its own colour scale and its own invoking figures. This is a late arrangement and a coherent one.
None of these is the akasha of Indian cosmology, and none is the ku of the Japanese godai. Both belong to five-part schemes with their own internal logic, and both are frequently glossed as aether in translation, which is how the conflation happens. The atlas keeps them as separate entities for that reason.
Sources On the Heavens (De Caelo)Aristotle with The Golden Dawn: The Original Account of the Teachings, Rites, and Ceremonies of the Hermetic Order of the Golden Dawn, 6th editionIsrael Regardie