I just came up with this, so feel free to add some stuff.
Everyone has a power in Erylin, a special power, unique to them. The most prized powers are ones to do with the elements, but they're very rare, a fire-wielder or water-bender showing up once a century.
In the land where our story takes place, there are two tribes, Rewera and Anahera, both having their own monarchy, their own justice system, law enforcement, land. They've been at war for centuries, hating each other so much, the word hate takes on a new meaning.
Rewera is all about enforcement, being strong and powerful, trusting only yourself.
Anahera is about community, loving one another, working together, "Being kind is better than being right."
Both have one thing in common: Scars and Black Stains
A black stain where your soulmate touches you for the first time. Anahera spend their lives searching for their True Love, while Rewera try to avoid their love love as much as possible. For them, love is a weakness.
Scars for how many people you've killed. For the Rewera, a mark of pride, for the Anahera, a mark of shame.
Is it complicated? I hope not. It's like a fantasy/war/soulmate type of thing, I guess. Also, I got the black stain thing from a pinterest post.
