Daemons of the Shadow Realm

Yuru lives in a remote mountain village with two ancient stone guardians overlooking the gates and his twin sister Asa locked in a cage at the village shrine. Asa, the only family he has left, performs a daily duty the elders refuse to discuss with him. The morning he finally pries the answer out of her, the cage and the duty and the guardians all stop being village curiosities and start being a tactical map of a much older war. Daemons of the Shadow Realm is the brothers' attempt to keep each other alive while the war remembers the village exists.