Threshing Day (The Empyrean) by Rebecca Yarros 

Welcome to Threshing Day, the brutal, high-stakes trial where would-be riders at Basgiath War College fight to earn the bond of a dragon or die trying. Amid ruthless competition and dragon fire, these thirteen cadets must survive a battlefield where desperate rivals will do anything to gain an advantage and dragons decide one’s ultimate fate—and where a single choice can forge a rider…or destroy them.

Xaden Riorson, the powerful leader. Rhiannon Matthias, the clever friend. Dain Aetos, the dutiful rule-follower. Liam Mairi, the kindhearted protector. Ridoc Gamlyn, the jokester. Sawyer Henrick, the underdog. Garrick Tavis, the dependable aide. Imogen Cardulo, the impulsive fighter. Bodhi Durran, the second-in-command. Mira Sorrengail, the fearless rider. Brennan Sorrengail, the brilliant tactician. Aaric Graycastle, the restless royal. Sloane Mairi, the determined sister.

On Threshing Day, there’s only one rule: don’t die.

The ebook edition of Threshing Day features fifteen beautiful original black-and-white illustrations by artist Joe Requeza.

The Empyrean series is best enjoyed in order.
Reading Order:
Book #1 Fourth Wing
Book #2 Iron Flame
Book #3 Onyx Storm