In Japanese traditional beliefs and literature, onryō are a type of ghost believed to be capable of causing harm in the world of the living, injuring or killing enemies, or even causing natural disasters to exact vengeance to "redress" the wrongs it received while alive, then taking their spirits from their dying bodies. Onryō are often depicted as wronged women, who are traumatized, envied, disappointed, bitter, or just furious by what happened during life and exact revenge in death. These kinds of ghosts appear extremely vengeful, ruthless, heartless, brutal, cruel, deranged, egotistical, selfish, bloodthirsty, and cold-hearted.

Sugawara no Michizane was a scholar, poet, and politician of the Heian period of Japan. He is regarded as an excellent poet, particularly in waka and kanshi poetry, and is today revered in Shinto as the god of learning, Tenman-Tenjin . In the poem anthology Hyakunin Isshu, he is known as Kanke (菅家), and in kabuki drama he is known as Kan Shōjō (菅丞相).