Legion

Silas Vane was a tactician condemned to die on the execution scaffold - until the soul-iron manacles binding his wrists became the instrument of his survival instead. Dragged into the Abyss, a fractured hellscape of warring factions, ash-choked fortresses, and a god-like intelligence sleeping beneath it all, Silas discovers he can do something no one in the Abyss has ever seen: bind souls to his will and forge them into a Legion.
To survive long enough to matter, he'll have to broker peace between warlords who've spent centuries trying to kill each other, win the loyalty of Thalia, a soldier too furious to stay dead, and face down the ancient Architect's design at the heart of the Abyss - a plan bigger and older than any single war. Legion is the origin story of a condemned man who becomes an army, a fortress commander who was never supposed to survive the drop, and the first chapter in a war that's only going to get bigger.