A remote mountain village wears the same silence that settled centuries ago. The shrine at its center hums with a presence the locals have learned to ignore. Yuru, a young man bred for a destiny he never asked for, breaks the quiet with his bare hands — a supernatural force shatters the seal, and his twin sister Asa is dragged into the Shadow Realm with no warning and no goodbye. The creature that took her is not a myth. It is ancient, patient, and it has been waiting specifically for them.

Yuru does not mourn. He moves. Beneath the shrine, a power called "daemon" stirs — beings neither holy nor infernal, bound by bloodlines and bargains that predate every kingdom on the map. He inherits one, and the cost is immediate: a voice in his skull, a hunger he must learn to leash, and the sudden, terrifying knowledge that the Shadow Realm is not a prison. It is a parallel nation. Asa is alive. And the war between the realm of light and the realm of shadow is not coming — it has already been waging for generations, fought by people who look exactly like him.

Also known as: Yomi no Tsugai, 黄泉のツガイ, Tsugai of the Underworld, Daemons of the Shadow Realm.