The Demi (An Acotar fanfic)

Based on the series by Sarah J. Mass.
Eretriana, a demiyana, a half-human, and half otherworldly creature, and the fourth Archeron sister. The adopted daughter of Miryam and Drakon, the heir to the throne of Cretea, home to the most advanced technology, weaponry, and armies in all of the world.
A beacon of hope sent by the ancient Gods, Demiyanas are the deadly peacemakers. More powerful than the Highlords' powers combined, able to kill instantly and fully control the death-lords, they serve as a barrier between the high lords and the innocent fae and humans caught in between.
Eretriana, only seventeen, has trained for this all throughout her short life. No one knew who she was until she stepped onto the battlefield. No one knew another Demiyana existed after the last one who lasted two thousand years vanished after the first war with Hybern. Everything changed the minute she vanquished tens of thousands of soldiers in a heartbeat. Everything changed hours before this when she snuck into the enemy camps. She changed forever.
After finding her soul sister, a bond that runs parallel to a mating bond, she yearns to find herself again and heal among the loss.
It's just war, they said.
The story follows Eretriana through the second Hybern war, ACOSF, and after.