Warrior and Witch

Warrior and Witch is also known as Witch (2008).

When a witch is born, a doppelganger is created. For the witch to master her powers, the twin must be killed. Or so it was believed for centuries...

Once Mirei discovered that merging with a doppelganger gave a witch more power than killing them, the witches at Starfall have been in an uproar. Her heresy goes against centuries of teaching – and the accepted practice of murdering their doubles

On a quest to collect the surviving doppelgangers, Mirei is unsurprised to discover that there are still witches at Starfall who side against her and her unorthodox ways. But worse, her fellow hunter and closest friend, Eclipse, has been captured by these same witches – and has no choice but to swear a blood oath to kill Mirei. If he fails his blood oath, he will die.

With the witches divided, and Starfall itself in the middle of a civil war, Mirei will have to choose between saving her friend and figuring out a way to unite Starfall before it's too late.