Katasumi begins with two Japanese schoolgirls who are caring for their school's rabbits. They are sweeping out the cages and feeding the animals when Kanna cuts her hand, and Hisayo leaves her to go into the school and fetch a bandage.

When she returns, Kanna is nowhere to be found. The rabbit cages are empty, and bits of blood and fur are strewn about. Hisayo then sees something that looks like a crawling woman (Kayako) begin to move towards her from the far side of the backyard. As she backs into a corner, she finds the body of Kanna amongst the debris from the damaged rabbit cages. She holds a trowel up defensively in front of herself while Kayako closes in upon her. Kanna then moves her bloody head, and looks on as the frightened Hisayo cowers in the corner and waits. The screen fades to black.

4444444444 opens with a young man (revealed to be named Tsuyoshi in the first Ju-on film) riding his bicycle home. As he rounds a corner in front of an apparently abandoned building, he begins to hear a cell phone ringing, though he cannot see it. He hunts through a garbage pile next to the darkened entrance to the building, finding the phone after several rings. Upon closer examination, the phone is displaying an incoming call from the number 4444444444. Tsuyoshi answers the phone to hear rasping, cat-like sounds issue from the earpiece. After unsuccessfully attempting to communicate with the unknown caller, he hangs up.

Seconds later, the phone rings again, and again he answers. Tsuyoshi is getting frustrated at this point, and begins to look a little worried, as though someone might be playing a joke on him. As he sits on the steps in front of the deserted building, he continues to try to identify the caller. Looking around nervously, he asks, "Are you... Watching me?" Suddenly, a voice replies, "I am," though it does not come from the phone. Tsuyoshi turns slowly to see a pale boy (Toshio) beside him, drumming white fingers on his knees. Tsuyoshi looks startled, and the camera lingers on Toshio for a moment before zooming in quickly while he opens his mouth in a cat-like scream as a black substance drips from it.