Which Side?

Astrid is a girl with a story. She is now 16 but her story starts when she is 12. She is a Protector that was left behind to be raised by her human parents. Until one day the Ruler of Shadows appears to her and convinces her to follow him. Astrid tired of feeling incomplete goes with him. She trains and once 16 she is allowed to go out on the field to put her training to the test. But on her first day on the field she runs into Protectors.
Protectors are the good side. They keep the balance in the world. Shadows set out to kill for fun. Astrid is the first Protector to be trained by Shadows. Protectors have stronger senses. The Shadows can travel anywhere they please at any time as well as fade into the shadows. Protectors only have their senses, strength, and weapons.