Introducing Empty Monsters by Cat Hellisen.
Aden Onnery is the eldest son of a family of midwives who use their power to eradicate magic. His whole life he has believed that the Onnerys destroy the monsters that will bring the end of his people, until he is forced to enter into a bargain with a magical survivor…
As a boy, Aden was never meant to take on the Onnery mantle, but an accident of birth has left him marked and strange
Now, in order to save his sister from the harsh law of the colonial powers, Aden chooses to enter the world outside his experience and go against everything he has been taught to believe.
He must help save the very thing his family are meant to exterminate—a magical lineage in his people.