Yam Fiend: a low-level monster that resembles a sprouting root vegetable with a angry face. It is not entirely clear where yam fiends come from, but they can be found in most temperate regions, and will aggro any person or domestic animal they encounter. Their leaves are a useful component in basic Cure potions.

Yellow Blade Grass: A communal creature native to the Kring plains, technically a cephalpod. A single stalk of blade grass resembles a three-sided pyramidal shell an inch or two wide, and up to three feet in height, with short roots or tentacles emerging from the bottom for locomotion. The edges are razor sharp, and they absorb fluids such as water or blood, through their shells. One is merely a nuisance. A patch several meters across is a threat to your herds, and the legendary Three-acre Blade Grass Patch unified the tribes to destroy a couple centuries ago. Generally, the larger a patch of Yellow Blade Grass is, the faster it moves.

Yotoden: The bamboo variant of the wood troll family. A corrupted Wood spirit has forged a bamboo grove into a single humanoid figure, and is animating it to lash out at pretty much everything. In addition to the usual strength, durability, and regenerative abilities, a Yotoden can fire bamboo culms at its enemies like bullets, with the added effect that they start growing if they manage to get inside the target's body. While the name is Yamato in origin, Yotodens have been encountered as far as the wild plains south of the Fang Empire.

Youkai: Fully demon-possessed warlocks specific to the Yamato Shogunate. While most demons do not cooperate well if at all, Youkai have a general consensus that a weak and chaotic empire does not have the resources to hunt them down and put their host bodies out of their misery.
A Youkai functions largely as a powerful spell caster, though they can if pressed manifest some of their supernatural physical traits.