I came across this list of various creatures from Japanese Legend that could be easily adapted to L5R to help keep thinks mysterious and mystical

https://en.wikipedia.org/wiki/List_of_legendary_creatures_from_Japan

A few more:

Busimin (Black Men): The busimin look a lot like humans but they have oily, pitch-black skins, bright golden eyes (that glow if the busimin is excited or agitated), and small, sharp fangs instead of teeth. They are uncivilized but not actively hostile, tho if their hunting-gathering lifestyle is disturbed (lack of food or competition) then they will become violent. Busimin show up in the Lion Lands and at the Crab/Unicorn border, but nowhere else. Their presence is tolerated in the Empire because they don't cause much trouble, but some Lion lords have developed an affinity for hunting them for sport.

Butagen (Pigmen): What is on the can. The butagen are pig-like humanoids living mostly in the Crab Lands and around the southern Crane Lands. They are actually civilized and somewhat hard to tell apart from very-very ugly humans. Since they have quite a resilience and a very high resistance against the Taint, the Crab maintains a secret "Butagen Army" and deploys it from time to time against minor Shadowlands incursions. Unfortunately, the butagen possess a pig-like behavior: they love dirt, revelry, and squeaking, making them quite an unpleasant company by human (let alone Rokugani!) standards.

Enjin (Monkey Men): It is also kinda like what it says. The enjin are essentially monkeys with an intellect of an adolescent human. They are loud and hyperactive but utterly terrified of conflict - an enjin will run rather than fight if provoked. They can be found in the Crane, Phoenix, and Scorpion Lands, and they are often recruited by entertainers to perform incredible feats of acrobatics and dexterity in public.

Guawa (Dragon Ogres): The guawa are fortunately rare sight in Rokugan as they are living in the northernmost parts of the Burning Sands. A guawa looks like a massive lizard, bigger than a warhorse, with an extremely muscular human upper body in place of the lizard's head and two tusks pointing forward from the back of its head. Members of the race are physically extremely powerful, cruel, savage, and arrogant. A pack of them can easily defeat a whole company of samurai, but it is a rare disaster to have them show up in Rokugan in such numbers.

Hanajin (Doppelgangers): The hanajin are shapeshifters, but unlike others of their kind, they can perfectly mimic not only living beings but inanimate objects too. In their natural form, the hanajin look like strange, multi-limbed humanoids with an assortment of tentacle-like appendages sprouting from their heads; their body is transparent and glows with a soft blue light, but they can change their color and suppress the light to meld into their environment like chameleons. Because of their shifty nature, contact with the hanajin is almost unheard of, and nobody really knows anything about this mysterious race.

Lamia: The lamia are a sub-species of the naga (similarly to the salamanders) and a true testimony of their adaptability. The lamia were naga who woke up early and decided to infiltrate human society rather than keep their distance from it. As such, they acquired a very specific mutation: their upper bodies turned perfectly human, indistinguishable from a beautiful rokugani man or woman. However this mutation and their extended cut-off from the naga race brought about a great cost: the lamia are almost completely cut from the Akasha, the naga hive mind, and thus are not considered a proper naga by the bloodlines.

Mogwai (Gremlins): The mogwai are essentially small, furry goblins. Big difference is that they are a lot more intelligent and are immune to the Taint. Because of this, they are the go-to minion/pet choice for eccentric Kuni shugenja and their like.

Nariphon (Dryads): Many rokugani scholars have tried to pin down this elusive race... so far, none succeeded. The nariphon look like small trees that distantly resemble (androgynous) humans and they can walk around and interact with their environment using root- and branch-like appendages. What makes them unique is that they grow from normal trees, resembling oversized versions of the tree's normal product until they "hatch" - the newborn nariphon will be then viciously protective towards its "mother tree" until a certain time comes and it wanders away, ultimately disappearing from sight. It is theorized that the nariphon and the daku no oni (a type of daemon similar to the nariphon) might be related: in the one reported case they encountered each other, the two went through some sort of merging ceremony, forming a healthy and untainted normal oak tree that had fiery orange leaves.

Sedu: The sedu is a race of centauroids, possessing a lithe body and four-jointed legs that allow them to reach incredible speeds. A sedu can outrace any horse, and they take great pride in their swiftness and grace, arrogantly looking down to anyone who can’t keep the pace with them. Contrary to their impressive physical traits, the sedu are not very bright and can be easily manipulated into unreasonable actions. Their tribes can show up on most rokugani plains but they are not native to these lands but wander into Rokugan from the distant Great Void.