Kayako Saeki is the main antagonist of the Grudge franchise.
Kayako's story is revealed in The Grudge 2. Kayako spend her childhood with her mother, an Itako (Japanese exorcist) who used her daughter to "eat" the evil spirits she drives away from her patients. This marks the child for the rest of her life, making her a target for gossip and cruelty. Kayako didn't have a father-figure in her life. When she attends university, she meets Peter Kirk, with whom she falls deeply in love. Years later, Kayako marries Takeo Saeki, the only person who understands and cares for her, and together, they have a son named Toshio. Eventually Kayako falls in love with him again. She writes of her feelings for him in her journal wich she kept all her life.
One day, Takeo finds and reads her diary. He becomes obsessed with the idea that Kayako is cheating on him with his son's teacher - or worse, Toshio could not be his son, but Peters's. When she gets home that day, he violently attacks her upstairs, pushing her against the wall. Toshio is in his bedroom drawing and hears the noise and, coming outside, watches the violence which is occurring below through the banisters. Kayako tries to run away while Takeo chases her, but he pushes her down. She sprains her ankle, stumbles and falls, and has to go down their house stairs by crawling. After much effort she makes it to the front door, only to find Takeo was slowly walking behind her, watching her pain. He then snaps her neck to a 90 degree angle. She sees that Toshio was watching the whole thing and starts to make weird noises. Even thoug her neck is snaped she is still alive but can't move. She sees Takeo dragging Toshio and eventually drowning him. After that she became an onryo and killed Takeo using her hair.