Caster by Elsie Chapman
Aza Wu understands the reality of magic--that it is illegal, and very dangerous. After all, it killed her sister, Shire, leaving Aza responsible for coming up with the money to pay off Saint Willow, a gang leader to whom everyone in Lotusland must pay tribute if they want to do business. However, when Aza is given a secret invitation to enter an underground casting tournament to win a prize that could change her life, she takes the chance.
Review from Booklist Starred Reviews:
The world is falling apart. Real magic, rare and potent, drains energy from the earth every time a spell is cast, leaving behind charred land, frozen oceans, and smog heavy in the air. Aza is secretly a full caster, but she hides her powers, pretending to be someone who can only do small, leftover magic. She's trying desperately to pay her family’s debt to sector boss Saint Willow before goons come to bust up her home and torture her family. Stuck in the shadow of her now-dead sister, Shire, Aza has one week left until Saint Willow's people come for her parents. When a note left by an old tutor leads her to an underground magic-fighting ring, she realizes she has the chance, the power, and the skill to get out from under Saint Willow’s thumb—possibly for good. The fighting ring leads to more questions still, as well as more danger. Could learning the secrets of magic and the truth behind her sister’s death be worth it all? Chapman (Along the Indigo, 2018) has created compelling young adult novels before, but this is a cut above; the fully realized and atmospheric dystopia is crafted at a level not seen often. This stunning fantasy will fly off the shelves.