Tomie Hashimoto is a dreamy and introspective high school student who escapes the boredom of her daily life by writing horror stories in which she imagines herself as a vampire named Ann Bathory. Shy and socially isolated, she is frequently bullied by her classmates. She lives alone with her loving but emotionally distant widower father, Kazuhiko Hashimoto, in a small, quiet town.

One day while admiring an ornate cross necklace in an antiquities shop, Tomie H. is approached by a strange and captivating girl her own age. The mysterious girl, who has a distinct beauty mark under her left eye, introduces herself as Tomie Kawakami. The two quickly become close friends, with Tomie H. enthralled by her new companion's confidence and charisma, even dedicating a character in her fiction to her. However, it soon becomes clear that their meeting was not a coincidence. Tomie K. has a hidden agenda that reaches into the past and is intimately connected to Tomie H.'s father.

Kazuhiko recognizes the girl as the same Tomie Kawakami with whom he was involved in a tumultuous relationship twenty-five years prior, a relationship that ended in her brutal murder. Despite this, he remained obsessed with her, even naming his own daughter after her. Now, Tomie K. has returned not just to rekindle his obsession but to terrorize his family. She manipulates Kazuhiko, attempting to convince him that his current life, including his daughter, is an obstacle to their reunion. The psychological pressure builds until Kazuhiko, wielding a meat cleaver, murders and decapitates Tomie K., disposing of her head in a nearby river.

The horror deepens when Tomie H. finds the severed head, which is not only still alive but also speaking. Demonstrating the supernatural regenerative abilities that define the Tomie curse, the head slowly begins to heal. Tomie H., driven by a desperate and misguided sense of friendship, takes the head home and tries to nurse it back to health, cooking meals for the growing body. This fragile and macabre arrangement is shattered after a violent argument, leading Tomie H. to throw the regenerating body off a building.

But Tomie Kawakami cannot be killed so easily. She soon reappears at the Hashimoto home, and Tomie H. shoots her with an arrow. Desperate to end the cycle of violence, father and daughter decide to freeze Tomie K.s body in a block of ice at the industrial freezer facility where Kazuhiko works, hoping to permanently stop her regeneration. The plan fails when Kazuhiko, unable to resist the frozen Tomies seductive pleas and cries, shatters the ice and frees her. Freed, Tomie K. attacks Tomie H. In a moment of ultimate betrayal, Kazuhiko locks his own daughter inside the freezing room, choosing the monstrous Tomie over his flesh and blood. As Tomie H. begins to succumb to the cold, she sees Tomie K. and her father walk away, holding hands.

The next morning, a worker finds Tomie H. and saves her life. Her father has vanished. Now living alone, she returns to her writing, finishing her story with a note of twisted hope: Ann and Mary are friends again. Ann will raise her to be a real friend. She then opens her desk drawer to reveal a dismembered, regenerating ear of Tomie Kawakami, a chilling indication that even in pieces, the immortal seductress is never truly gone and her influence persists.