Chapter 2 of Tomie Part 2.
Following on from the events of chapter 1, rumors of Yukiko's operation and the "kidney monster" have spread all over Morita Hospital, including the report that the monster is now being kept in the basement. A teenage boy named Fumihito asks his nurse if the stories are true and she says no; but then he sees her sneaking down to the basement. He follows and overhears the doctors talking about everything, including the fact that they are keeping Tomie's head for observation. Fumihito also hears Yukiko's name.
Fumihito goes to find Yukiko even though she is not allowed visitors. Yukiko at first thinks he is Tadashi, because they sound alike. A doctor catches him and forces him out of the room. Yukiko's doctors later discuss her condition and that she has already completely recovered, just two days after major surgery. They consider the implications of having the head inside her, as it was over a month until Tomie was removed.
Fumihito continues to visit Yukiko, and develops feelings for her. Meanwhile the doctors discover that Yukiko's body is infected with cells from Tomie. They experiment with radiation to see if it will kill the cells; but it instead accelerates Tomie's regeneration. She calls out to Dr. Tamura and tries to seduce him. He is horrified and orders the basement to be locked.
Fumihito, curious about the basement and desperate to help Yukiko, goes down to the basement and breaks in. He finds a naked Tomie, now fully regenerated, inside the tank where she was kept after being removed from Yukiko. Tomie goes up to Yukiko's room and threatens her, but Tamura catches her and realizes that she has regenerated in one day. She escapes from the hospital.
The doctors had expected Tomie's presence inside Yukiko to cause cancer and kill her, but discover it's caused other changes. Yukiko has become taller, more attractive, and her hair has started to grow rapidly. She flirts heavily with Fumihito but he rejects her, put off by her newfound vanity. She becomes angry at him and he tries to run away from her, but collapses in pain because he's still recovering from surgery. Yukiko laughs at him and insults him, planning to find Tadashi after she is released from the hospital tomorrow. Back in her room, she wonders what came over her, and notices that she now has a mole under her eye just like Tomie's.
The doctors had taken cells from Tomie to experiment as regenerative medicine, but the fully grown Tomie sneaks into the basement and burns it to prevent it from growing into another version of her. She also reveals that she had seduced Tamura and is living with him. Tamura traps her in the basement and says that since she destroyed his research specimen he'll have to experiment on her instead. The fire begins raging out of control. Takagi has been lying in wait at the hospital and realizes his plan failed - he simply wanted the doctors to experiment on Tomie. He decides the hospital must be destroyed and pours petrol all over, causing the fire to spread rapidly. Fumihito goes up to Yukiko's room and tries to get her to safety. She has now fully transformed, and tells him her name is Tomie. She escapes from the hospital.
The bodies of the chief doctor, Tamura, and "an unidentified woman" (the Tomie removed from Yukiko during the operation) are found in the hospital's basement. It closes its doors forever, and all the nurses involved in Yukiko's operation eventually meet untimely deaths. Fumihito wonders where Yukiko went.