Three
The Number Three is a sacred number to many of the native inhabitants of the island. In Old Yuriban texts and to some extent into the current age the number three continues to permeate Yuriban society and lore. In many Yuriban legends and myths events and unity occurs in factors of three. Particularly within Goddess myths the number three is a highly noticeable trend. The most common myth containing the number three being the tale of Akibimi and Engetsu's fall from the bridge. Chikyuu fulfills the role of the Third when she takes the pair into herself as mountains to save their lives.
Some incomplete texts pertaining to the Guardians (the few that have been found) contain many references to the number three as well. Though in what capacity it is hard to tell.
The number three also explicitly applied to the Inishie cultists who appeared during the Eruption of 2012, mainly in that their group was comprised of three cultists forming a so-called "Doom Trio."