I’m on mobile so I’m not even going to try and quote and delete all of that to get to the part I actually want to talk about.

The Sai Taisui are shikigami created by Geomancers. They are the same as the Koja and shikigami you meet throughout Stormblood. Except, they can only be created with mud collected where the leylines of water, earth and wind Aether intersects. It’s why they really show up at Swallow’s Compass (because they dungeon was created at the specific spot in Yanxia for this reason.)