[1][2][3][4] Kayako's fictional history alternates slightly between continuities, but all depict her as the very attractive yet unfortunately vengeful ghost of a woman killed by her husband, Takeo, along with their son Toshio, in a murder–suicide that happened after he came to believe she was having an affair.

The American adaptations expand the backstory of the character, with her only cameo appearance occurring in the 2020 film, where her "grudge" is transferred to other spirits.

In the (Ju-on timeline), as revealed in the official novel written by Kei Ohishi, both of Saeki's parents were present highly neglectful, causing her to feel depressed and lonely.

After the accidental deaths of her parents which did not seem to faze her, Kayako marries Takeo Saeki, the only person who understands and cares for her, and together, they have a son named Toshio.

She writes of her feelings for him in the journal she kept all her life; in most variations of the story, Takeo ends up finding and reading her diary.

The psychic, Keizo Tokiwa, intended to have Kayako battle Sadako and have them destroy each other to free their current and future victims from their curses.

At the same time, however, after spiriting away four schoolboys, Suzuka believes she sees one of them in the house late at night and goes there to check on him, only to have her parents follow after her as well.

Kayako was quickly warded off with an essence of Sadako's spirit for Keizo, Yuri, and Tamao to save Suzuka.

Therefore, the primary reason for her becoming an Onryō in The Grudge is because of the malevolent spirits she was fed by her mother, and not purely because of the painful nature of her death.

Peter Kirk, a man she was obsessively in love with, finds Kayako's body in the attic and commits suicide soon afterward.

Naoko then shockingly turns into a vengeful Onryō as well, despite her mother not feeding her evil spirits like she did Kayako, and kills her attacker.