Demon

Demons are manifestations of grudge and are parasitic entities of the movie Princess Mononoke.

Beings infested by demons are called Tatari Gami (タタリ神, tatari-gami, lit. "cursing gods") in Japanese.

Appearance
Demon worms are red/black, maggot or snake-like beings resembling congealed blood that emerge en masse from creatures turning into demons. They lack visible eyes, but appear to have a mouth similar to that of a leech or lamprey.

After Tatari-Gami is killed, their flesh rapidly melts away, leaving only bone.

Cause


Lady Eboshi uses toxic cannon ammunition and Jigo's tracker uses the poison, too. The poison weakens the flesh. Then the victim loses control of itself because of pain and agony, and turns into a demon with hatred only in mind. As the victim goes mad, demons worms manifest.

Ashitaka is infected and marked after fighting Nago, but strangely doesn't become a demon. Instead, he is granted with power, which eats at his lifespan when used. In order for one to become a demon, they must already harbor hatred in their heart, which Ashitaka did not. As Ashitaka continually uses his power, the black growths cover his skin, showing the progression of the disease.

Plants, however, cannot become hosts for demons, and instead instantly die on contact.

Cure
There is no known cure besides the blood of the Forest Spirit, and intervention must happen before the full demonization or death of the victim.

Clean water is known to temporarily alleviate the effects of the curse. Ashitaka and San are cured of their affliction upon being engulfed by the Forest Spirit when returning its severed head.

It is unknown if a 'true' demon such as Nago can be cured.

Victims
Two characters became Tatari-Gami: Three more characters were infested by demons:
 * Nago
 * Okkoto
 * Ashitaka
 * San
 * Moro

Trivia

 * The Demon worms were animated by Haru Matsuda.
 * Tatari-Gami's general appearance is a presumable reference to Tsuchigumo, a term refers to either monstrous spider-like yokai or renegade local clans including Emishi.
 * It is possible that Nago wasn't the first Tatari-Gami to attack Ashitaka's village or areas in vicinity as Ji instantly identified Nago to be a Tatari-Gami, suggesting that either Ji has directly seen other case(s) or Ji heard about the demons in the past.
 * It is possible that they were inspired by the California Blackworm.

Rachegott