Sōma

Sōma is an ethereal demon spirit that takes the form of a deer skull with a blue aura.

Four-hundred years ago, Sōma almost destroyed the Daidai Village, leading them to waste away. It was confronted by a shrine maiden named Kuen. She managed to seal the demon inside of her body. However, with the rapidly draining memories in her, Kuen failed to slice off both emerging horns to complete the seal. Instead, it was sealed in a nearby rock with a portion of it staying within Kuen. Sōma's curse left Kuen forever purged of her memories. It also resulted in a curse that was passed down to her descendants. When two bearers of the curse reach age twenty, the curse manifests a mark on the palms of their hands, signalling they connect Sōma with the outside world, and they slowly have their memories drained. Every hundred years, the seal that restricts Sōma weakens and its horns begin growing from the rock and it becomes stronger. In order to prevent Sōma from escaping the seal, a man and woman who each bear the curse, must be wed to reapply the seal.