The title of the Japanese films translates roughly to "Curse of Grudge", or more abstractly, a curse created due to an individual bearing a grudge against someone or something. The first two films in the series were so-called V-Cinema, or direct-to-video releases, but became surprise hits as the result of favorable word of mouth. Both films were shot in nine days and feature a story that is a variation on the classic haunted house theme, as well as a popular Japanese horror trope, the "vengeful ghost" (onryō). The titular curse, ju-on, is one which takes on a life of its own and seeks new victims. Anyone who encounters a ghost killed by the curse is killed themselves and the curse is able to be spread to other areas.
Although her background is significantly different between them, in all versions Kayako is an onryō - the furious, spiteful spirit of a Japanese housewife who was brutally murdered by her husband, Takeo, after his discovery of her secret feelings towards another man. This insane act gathered a grudge curse at the murder setting, their house, that condemns anyone who steps inside to succumb under Kayako's spreading anger.
The murders eventually gathered a grudge curse in the Saeki house. Mr. Konishi, Toshio's teacher, visited them after Toshio's unexplained absence from school. He met Kayako, who behaved strangely and repetitively told him Toshio was "resting". After Konishi was taken by the curse, the substitute teacher Yui noticed Toshio's absence and visited the Saeki house as well. Kayako invited her in and Yui asked for Toshio's whereabouts. Kayako only told her "his father took him" and that he would be back soon. Yui went upstairs looking for the boy until a rattling Kayako scared her away from the house while filling her journal's pages with spirals. Yui told the school's director that something was "not right with that woman". One night, Kayako manifested to Yui and left the journal to her. At home, the ghost possessed Yui, who was later found by her boyfriend Naoto. Naoto noticed the journal and throughout its pages discovered Kayako's strong desire to be a mother. Worried about Yui, Naoto started investigating the Saeki family's past and uncovered the mystery between the two Toshios, until the ghosts of the mother and son appeared. Kayako's ghost broke his neck, with Yui finding his body afterward. Yui returned to the house and found several videos of Kayako's life with Takeo and Toshio, and had a vision of her revelation and murder. When Yui found what seemed to be Kayako's corpse up in the dark attic, the ghost then moved and pursued her downstairs.
With the grudge curse born, Kayako made several people that entered the house her victims. Later, she showed Karen Davis, a girl who had discovered about her past what caused her death and anger through a vision. Karen, after she set the house on fire in order to stop the curse, had one last vision, of the Saeki family as if they were alive and happy after all, only to be surprised by Kayako while in the hospital, realizing that her grudge would never stop. Karen, however, kept her belief that she could detain it and resisted, until she was caught by Kayako at last. 781b155fdc