Sōma

is a demon that consumes memories from its victims.

Background
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.

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

Abilities
Sōma is able to steal the memories of whoever it comes in contact. Alternatively, it can possess people, altering their personality to do its bidding and likewise channel its power through the target. He is also shown to be intangible, physical attacks and most ninjutsu simply pass through him without harming, although sealing barriers can immobilize him.

Konohamaru's Love Arc
As the seal began weakening again, Sōma lured and tricked Kankitsu Akitsuki, Remon Yoimura's fiancé, into its chambers where it possessed Kankitsu. Using its new pawn, Sōma was able to break the seal fully and escape. Its rampage was halted by the appearance of Konohamaru Sarutobi and Boruto Uzumaki. While their efforts could not defeat Sōma, Remon used the same ancient seal of her ancestor Kuen to seal Sōma in her. Through the aid of the reluctant Konohamaru, the emerging horns were severed, completing the seal and permanently trapping Sōma.

Legacy
While Sōma was finally defeated for good thanks to Remon and Konohamaru, the efforts left Remon forgetting all she knew before the seal.