Tsukiko Izumikawa, a quiet high school student and member of the photography club, has always lived in the shadow of her older stepsister, Tomie. Beautiful, charismatic, and effortlessly popular, Tomie possesses an intoxicating allure that captivates everyone around her, including Toshio, the boy Tsukiko secretly loves. One evening, while Tsukiko is taking photographs of Tomie and Toshio, a steel beam falls from a nearby construction site, crushing Tomie’s neck and killing her instantly before her younger sister’s eyes. One year later, Tsukiko’s life has slowly returned to a fragile normalcy, though she remains haunted by nightmares of the accident. On what would have been Tomie’s 18th birthday, her family gathers to commemorate the day, only to receive a startling visitor at the door. Tomie has returned, appearing even more radiant and captivating than before. While her overjoyed parents welcome her back without question, Tsukiko is immediately disturbed, sensing that something is profoundly wrong with her resurrected sister.

The story is set primarily in a contemporary Japanese suburban town, shifting between the Izumikawa family home and the local high school. The initial conflict arises from Tsukiko’s growing terror as Tomie’s behavior becomes increasingly bizarre and malevolent. Using her supernatural charm, Tomie manipulates their father into violently punishing Tsukiko for her perceived lack of affection. The horror escalates when Tomie reveals a grotesque, pulsating tumor on her neck where the fatal injury occurred, a tumor that soon develops a chattering mouth and a malevolent consciousness of its own. When Tsukiko recoils in horror and calls her a monster, Tomie attempts to flee, but their father stabs her to death with a butcher knife. The following morning, Tsukiko witnesses her mother calmly dismembering Tomie’s body in the bathroom. Her mother disposes of the head in the trash and, while preparing Tsukiko’s school lunch, unknowingly mixes fragments of Tomie’s flesh and hair into the food.

At school, a new student arrives who looks exactly like Tomie, while Tsukiko discovers miniature, living Tomie heads growing inside her lunchbox. Her best friend, Yoshie, is murdered by these tiny creatures when she investigates the discarded lunch. Back home, the severed head of Tomie rises from the trash and convinces their father to kill his wife and feed her remains to it. The narrative then fractures into a surreal nightmare, with Tsukiko witnessing the violent deaths of her friends and classmates, including a scene where Yoshie’s headless corpse attacks the judo club. Tsukiko herself stabs Toshio to death and finds herself cornered by multiple clones of Tomie in a locker room. Just as she is overwhelmed, she wakes up in her bed. Her parents now claim she has always been an only child, and for a moment, Tsukiko believes it was all a dream. This reprieve is brutally cut short when her father begins compulsively eating his own hair and her mother’s head stretches grotesquely. A giant, monstrous Tomie head has taken over their living room, and carnivorous centipedes made of fused Tomie heads swarm the house. The nightmare logic reveals that Japan is being overrun by these immortal, seductive creatures. In a final confrontation, Tsukiko is consumed by the centipede swarm and emerges from her home transformed, having become another Tomie. She walks through streets filled with identical women, approaches a stranger with a smile, and is shown being murdered by him. As she lies dying, her reflection in a mirror remains that of her original stepsister, who asks if she is finally happy, before Tsukiko’s original personality is completely replaced. The arc concludes with the implication that the Tomie phenomenon is not a single entity but a limitless, self-perpetuating plague of immortality and horror.