The Demonic Spirit is the main antagonist of Samurai Jack episode "Jack and the Haunted House". It is a dark phantasmal creature who cursed a house and the people within it.
The Demonic Spirit's past is unknown, but what is well known is that the spirit has devoured more than just Kuni's family. At some point, it took completely over her house devouring her family souls but instead of taking her as well, it decided to use the girl for its own benefit by making her drive more people to the house so the spirit could take more souls of innocent people.
When Jack met Kuni he also fell into its trap. Jack fought with all his effort to defeat the demonic spirit but was shortly defeated and his soul was devoured. However, Jack found himself in the demon's realm where it had all the souls of the victims it had consumed and engaged in a battle against the demon in its physical form. Jack finally destroys the demon for once when he deflects the demon's dark fireball back to it releasing the souls of the people it consumed. Back to the reality, Kuni reunites with her family and the house is purified from the demon's influence.
- The spirit is one of the few antagonists who has no relation to Aku.
- While only appearing in one episode, the monster is regarded as the most terrifying enemy Jack has fought.