The Legacy of Tril: Soulbound

Sixteen year old Kaya is a Healer. She lives in Tril, a world where Barrons fight an ongoing war against the evil Graplar king, and Healers tend to the Barrons when they are wounded. Healers and Barrons are bound to each other, either from birth (Bloodbound) or during a special ceremony (Bound). Healers can cure their Bound or Bloodbound Barrons almost instantly with a touch.
Kaya wants to learn to fight as well as heal, but in Tril, and at her school, the Shadow Academy, she is not allowed to. Therefore, she must learn to fight in secret, and first asks her Bound Barron, Trayton, to teach her. Trayton is sweet and brave and Kaya finds herself falling for him, but he's a rule-follower and will not train her. Then she meets Darius, a young man with a mysterious past who trains the Barrons at the Academy. He agrees to train her, but from the moment they meet, they are at odds and have a fighting, sarcastic relationship.
Meanwhile, despite the safety of the Shadow Academy's surrounding outer wall, several Graplars—horrible monsters under the control of King Darrek—invade the school. Kaya is determined to find out how they got in and to stop them, with whoever's help she can.