Fallen Academy (Year One) by Leia Stone

First in the popular Fallen Academy, a compelling crossover series that sits in the sweet spot of romantasy and dark academia, with an apocalyptic war between angels and demons thrown in for good measure. Get ready for your newest fantasy obsession. When angels fell from the sky to war with the demons that ravaged Earth, their combined powers infected humanity. Now, the humans are assigned one of two fates: demon gifted or angel blessed. After wings sprout from Brielle's back at her awakening ceremony, she's sure she's an angel-blessed celestial—until she sees black wings and realizes something is terribly wrong. Having sold her contract at a young age to save her father's life means she should be bound for Tainted Academy. That is, until a fallen angel unexpectedly fights for her to be accepted into Fallen Academy, the elite school for those that inhabit Angel City. She's immediately matched with her impossibly handsome celestial teacher Lincoln Grey. Laying eyes on him, her first thought is that her time at the academy might actually be fun, but this theory quickly fades when she and Lincoln clash on day one. To further prove her admission into Fallen Academy is cursed, the entire school is thrown into chaos when an Abrus demon reveals that he knows Brielle's secret. Now, above all else, Lincoln must fight to protect her—and fight his feelings for her.