Smoke & Summons By Charlie N. Holmberg

As a human vessel for an ancient spirit, Sandis lives no ordinary life. At the command of her master, she can be transformed against her will into his weapon—a raging monster summoned to do his bidding. Unlike other vessels, Sandis can host extremely powerful spirits, but hosting such creatures can be fatal. To stay alive, she must run. And in a city fueled by smoke and corruption, she finds a surprising ally.
A cunning thief for hire, Rone owns a rare device that grants him immortality for one minute every day—a unique advantage that will come in handy in Sandis’s fight for freedom. But Sandis’s master knows how powerful she is. He’s determined to get her back, and he has the manpower to find her, wherever she runs.

Now, to outwit her pursuers, Sandis must put all her trust in Rone and his immortal device. For her master has summoned more than mere men to hunt her down…