Bù refers to the remnants of a tradition of Twinsun's ancient past. It seems that Bù flourished in or near the present-day location of the Desert Island. Bù was/were an ancient source of the Legend of Sendell.
As it is not explained who or what "Bù" was, one can only speculate about it or them. It seems that Bù was an ancient civilization, people, species or even a religion or set of traditions. Another possibility is that Bù was a region, a lost, ancient country or location somewhere around the Desert Island. It's also possible that Bù was a person, a religious or historical figure, deity, wiseman or ruler, who established that culture.
Relics remained as legacy of Bù are:
- The mysterious Temple of Bù in the White Leaf Desert
- The Book of Bù, which prophecies the coming of a dictator, the Heir, and describes the actions of the Heir to defeat him.
- The statue of a "Bùian mermaid" which was found in the middle of a desert (possibly White Leaf Desert). It was taken to the Maritime Museum, described to represent the "absurdity of ancient superstitions".