Tear Down Heaven by Rachel Aaron

Five thousand years of war and rebirth have all come down to this.

Bex and her army have made it to the precipice of Gilgamesh’s Heaven. They’ve occupied the white mansions, taken the golden streets, freed the house slaves of Heaven’s warlocks. The final fortress of the enemy stands right in front of them, but the demons’ fight is far from over.
Though she defeated the Queen of War and freed her people from the Hells, Bex’s sword is still silent, her horns are still missing, and her army is little more than a mob of terrified former slaves who can barely stand. What the demons need most are rest and recuperation, but time is not on their side. For all the battles they’ve won, Gilgamesh hasn’t stopped racing toward the culmination of his grand—yet still unknown—ambition, and he’s not about to let Bex’s ragtag rebellion get in his way.
To save her people and reclaim their ancient home, the Queen of Wrath is going to have to take the fight to the enemy. It’s finally time to end the war the Eternal King started five thousand years ago.
It’s time to Tear Down Heaven.