The amanojaku or amanjaku (天邪鬼, "evil heavenly spirit") is a yōkai of Japanese folklore.
He is usually depicted as a sort of small oni and is said to have the power to provoke a person's darkest desires and, therefore, incite him to perpetrate wrongdoing.
One of the best known appearances of amanojaku is in the fairy tale Urikohime (瓜子姫, "melon princess"), in which an elderly couple cherish and shelter from the outside world a girl miraculously born from a melon.
One day, she naively let the amanojaku enter their home where he, according to the versions, abducts or devours her and sometimes pretends to be her by wearing her flayed skin.
It is generally agreed that the amanojaku originates from Amanosagume (天探女), an evil deity of Shinto mythology, who shares with the amanojaku the unnatural ability to see into people's hearts.
According to other sources, the myth of amanojaku was introduced in Japan during the Yamato period at the time of the spread of Buddhism.
The first traces in Japanese literature of the amanojaku date back to the seventh century where it is mentioned in the Kojiki and the Man'yōshū.
The creature's introduction into Buddhist beliefs may have been through syncretism with the yaksha, which is considered an opponent of Buddhist teachings.
She is commonly depicted as being trampled and subdued to righteousness by Bishamonten or one of the other Shitennō. In this context, she is also called a jaki (邪鬼).