Dream Creatures: They act as guardians of dreams. Each person has one but is unable to see it in reality but only in dreams. Dream creatures also feast of ones dreams when they feel hungry (and that’s not often) which is why people sometimes can’t remember the whole or a part of the dream when awake. When people don’t get enough sleep the creatures tend to fall ill and become unable to protect the owners in the dream, resulting people to have nightmares. That, or dream creatures get lazy and neglect their jobs…
Dream creatures can roam free in Dimension 4 (and in this case Mugen as well, only if you own one and know how to summon it out of your mind) or dreams of their owners, never in someone else’s.
I know my anatomy isn't quite the best but I felt like this needs to be done. It's not really the properest reference for Suna but this is the best I could do for now. There are tons of spelling and grammar errors so forgive me for that, I couldn't check those up.
Here are few more facts about Suna and Dream Creatures:
-Dream Creatures can eat both good dreams and nightmares. If they feel protected of their owner (and that purely depends on their personality) they will eat up the nightmares that could bother the dreamer. If not then they are either too lazy, not willing to do so or dead.
-When Dream Creature is facing an enemy, it's instinct is to make itself as scary as possible: The ear stand upwards, the fur, tail and head are raised high, it starts to hiss and growl with it's jaws wide open and would make sudden warning moves (jumping forward a bit, claiming more space to show who is the boss).
-While most people aren't able to see Dream Creatures, they can still run into it while dreaming but people usually get scared of them since they all look like monsters.
-Because Aya loves to sleep, she met Suna way before she learned she can "summon" her spirit outside of her mind. They bounded trough dreams and one day Aya was able to see her (as a ghost) and thus they are inseparable.
-Just like Suna owns some accessories, other Dream Creatures can own some as well (again, depending on their personality).
-When the owner dies so does the Dream Creature but Dream Creature can also pass away from starvation (self done or from the side of owner when not dreaming enough).
-The only way Dream Creature can outlive it's owner is if it knows how to form itself as a spirit and has a super strong drive/reason to stay alive (usually revenge). If living as such for too long it can "evolve" itself into a Nightmare Beast: Creatures who can also be origins of Hellhounds, if strong enough to get use to not eating dreams but stay alive trough feeding from fear or souls. This is very rare.
-Dream Creatures are usually very tall, about 2 meters or less high when standing normally.
-They are also known for their incredible stamina. They may look skinny but feeding off dreams keeps them strong and in shape for any physical activity (if they eat when necessary of course, otherwise they will grow weak or sick).
-As mentioned, their tongue is used to pick up dreams (same way giraffes pick up leaves with their tongues). When they eat the dreams seem to appear a lot like cotton candy, so their tongue is necessary for picking them up, putting them in their mouth and swallowing. Their sharp teeth are used mainly for defense (dreams can be a dangerous place).
-Dream Creatures CAN'T invade some else's dreams/nightmares but only the ones of their owner.
-When not roaming the mind and dreams of their owners, Dream Creature can spend time in Dimension 4. This is where they have contact with other Dream Creatures.
-They don't need a special type of breeding, when a person is born, eventually, so is another Dream Creature. They are created purely form someones mind/imagination and while they aren't real in reality, they are a fully living creatures in another dimension/world/wavelength.
-Suna is, by gender only, a she, because Aya is by gender (and sex) a she. Since dream creatures don't breed with one another they trace off the gender of their owner, and by gender only. So when the owner may be a male but by spirit feels like a female, the gender of a Dream Creature will be a female, and vise verse. But they don't find this very important among each other since, aside from the listed verities, they don't have sexes to tell them apart, only maybe voices and and owners gender (which isn't always so accurate) so they are called "it" most often.
Will insert more info in artists comment if needed.