After spending 3 hours inside the Library, I've already skimmed through most of the books stored inside. From History to Geography to Theories about Spells and Elements.
There's also no books about Aether or Void save for one which is titled 'What is Aether and Void?'. It's a book written by an old Elemental Fusing Realm who dabbled on his research about the two Incomprehensible Elements.
According to the book, Aether and Void might be totally nonexistent or it could only be perceived under special conditions. And if it's the latter, it mentioned that Aether could probably be perceived if someone's affinity to the 4 Natural Elements and 2 Special Elements reached a certain threshold.
The book called the Aether as the essence of everything and that it exists among everything in the world. Be it living or non-living things.