By the Pact (Pacts Arcane and Otherwise Book 1) by Joanna Maciejewska
High mages lied: Veranesh, the demon who destroyed the continent is still alive. And it's up to their former student to expose the truth—even if it means another Cataclysm. When Kamira, a once high mage student turned arcanist, discovers an imprisoned demon in underground ruins, she is forced into a pact that grants her powerful magic, but also ties her to the very demon that once devastated the continent… and Veranesh wants his freedom. With one friend by her side, Veelk, a mage killer bound on protecting her, Kamira will have to outwit the archmages, other demons, and possibly her own demonic benefactor to survive. Her chances are slim, but with Veelk’s ever-present sarcastic repartee, Kamira might just pull through. Plots and schemes, power and means—sometimes the price for victory is choosing which friend will die, but when you only have one friend, the choice is… easy?
Book Length: Long Novel - 320-650 Pages