Kodoku, also called kodō, kojutsu, and fuko is a type of poisonous magic found in Japanese folklore. It is the Japanese derivative of the Chinese Gu magic. To create kodoku, sorcerers would mix several insects in a jar, and let them kill one another until only one survived. The fluids of the insect that survived would be used to poison an individual with a curse that would control them, cause them misfortune, or kill them. The remaining insect could also be used as a sort of "luck charm" granting the one who performed the ritual great wealth. In return the owner is supposed to feed the bug. Neglecting to do so would enrage the insect, if the owner does not equivalently repay the insect by placing all his or her riches beside a road, plus interest in gold and silver, the insect would devour the home owner. Therefore, this ritual could also be used as a death curse by giving the riches to an ignorant individual. The term "kodoku" can also be applied to the spirit which is the incarnation of this particular magic. The technique was used in the Nara Period.
In fiction
The technique plays an important role in the first part of the 1985historical fantasy novel Teito Monogatari. The protagonist Yasunori Katō is a master of kodoku magic and uses it to manipulate his victims. The spirit is represented as an insectoid worm which lives in the stomach of the victim.
The term "spiritual kodoku" is used in the anime Ghost Hunt for a curse technique in which spirits are trapped like insects are in traditional kodoku practice. A dominant spirit devours the weaker spirits until it has enough power to kill the target of the curse. The only way to stop the curse is to "feed" the spirit as compensation.
In InuYasha the main antagonist Naraku creates a kodoku inside a mountain to gather and merge hundreds of yōkai to form a new body for himself.
Kodoku is used in the anime Fushigi Yûgi as a drug to change the personality of one of the major protagonists, Tamahome.
The Kagewani from the anime of the same name is a shadow creature that was created through kodoku using several different animals instead of insects.
In Ōsama Game: Kigen, a manga prequel of Ōsama Game, the culprit behind a murderous game is subsequently revealed to be a virus, created through kodoku by Natsuko Honda's ancestors.
The idea of Kodoku is a central motif to the plot of the manga BIOHAZARD Heavenly Island, where it is used by the main antagonists to develop a new B.O.W.
In the Web Novel Re:Monster, Kodoku is used by the main protagonist as a method to create a more powerful army, from pitching many different summoned creatures against each other inside a hole, and letting them "evolve" by themselves.
In "Mob Psycho 100", one of the minor antagonists, Matsuo, uses Kodoku to merge evil spirits to create powerful "pets".
Hunter x Hunter succession arc is based on this ceremony
