Wrath

Wrath by John Gwynne
The Faithful and the Fallen #4
The final war is here.
Tropes: Final Battle, Betrayal, Found Family, Sacrifice
 
The Banished Lands are engulfed in war. King Nathair, now in possession of three of the Seven Treasures, aims to open a portal to the Otherworld, unleashing the demon Asroth. Corban and his allies must rally the remaining forces to prevent the world's end. As alliances shift and sacrifices are made, the fate of humanity hangs in the balance.