Tomie Hashimoto is a dreamy teen who writes homo-erotic horror fiction in which she imagines herself as Ann Bathory, a vampire. Introspective and lonely, she is picked on and bullied by her classmates at school, and lives alone with her loving, yet distant widower father, Kazuhiko Hashimoto. One day, while admiring an ornate jewel encrusted cross necklace in an antiquities shop, Tomie meets a strange, beautiful girl with a mole under her left eye. The mysterious stranger says her name is Tomie Kawakami. The girls become best friends (with heavy lesbian undertones) and Tomie H. dedicates the character of Mary from her fanfiction to her new friend, but it soon becomes clear that the two girls meeting each other was not purely accidental. Tomie Kawakami has an agenda, and it involves Tomie's father.
It is revealed Kazuhiko was involved in a relationship with Tomie many years ago which resulted in her being murdered. However, Kazuhiko was still obsessed with Tomie and even named his own daughter after her. Tomie is back to terrorize his family and tries to convince Kazuhiko to murder his daughter. Kazuhiko ends up murdering and decapitating the other Tomie, and throws her head into a nearby river. His daughter, Tomie Hashimoto discovers the talking head and nurses Kawakami. back to health as she regenerates. She spends a lot of time cooking and taking care of her but after a brief argument between the two, Tomie Hashimoto ends up throwing the regenerating Tomie body off a building.
Soon afterwards, Tomie Kawakami shows up at her front porch and Tomie H. shoots her with an arrow, killing her. She and her father freeze Tomie into a block of ice to prevent her from regenerating and coming back to life, but after hearing the frozen Tomie's pleas and cries Kazuhiko breaks the block of ice and sets Tomie free. Tomie Kawakami then attacks his daughter but gets hit in the head by her, which results in Kazuhiko locking his daughter into a freezer room. Tomie laughs as she and Kazuhiko walk away, holding hands. The next morning, Tomie Hashimoto is discovered by a worker from the ice sculpture company who saves her life.
Tomie Hashimoto is now shown living alone, with her father missing, albeit thankful because she believes he tried to save her from the other Tomie, which is the reason he teamed up with her and abandoned his daughter. Tomie goes to her room and continues writing her fanfiction. She writes: "Ann and Mary are friends again, there'll be no issues this time. Ann will raise her to be a real friend, a friend whom she can depend on". Tomie then opens her desk drawer and looks at a dismembered, regenerating ear.