We Are the Fire by Sam Taylor

In the cold, treacherous land of Vesimaa, children are stolen from their families by a cruel emperor, forced to undergo a horrific transformative procedure, and serve in the army as magical fire-wielding soldiers. Pran and Oksana―both taken from their homeland at a young age―only have each other to hold onto in this heartless place.

Pran dreams of one day rebelling against their oppressors and destroying the empire; Oksana only dreams of returning home and creating a peaceful life for them both.

When they discover the emperor has a new, more terrible mission than ever for their kind, Pran and Oksana vow to escape his tyranny once and for all. But their methods and ideals differ drastically, driving a wedge between them. Worse still, they both soon find that the only way to defeat the monsters that subjugated them may be to become monsters themselves.