Toshiaki Nagashima Hiroshi Mikami is a researcher who studies mitochondria and explains how they pass down from mother to child and how they might be used for tissue regeneration through the liver. On their anniversary, his wife Kiyomi Riona Hazuki visits his lab, only to discover he has forgotten the date. During their drive home, Kiyomi is involved in a car crash and is left in a coma with brain damage. A doctor, Takashi Yoshizumi Tetsuya Bessho meets Nagashima the next day and tells him his wife was an organ donor, and that a young girl named Mariko Anzai Ayako Omura in the hospital needs a donor kidney. He agrees to donate her kidneys on the condition he can have Kiyomi's liver. Nagashima takes the liver to his lab, dismissing the scientists so he can perform experiments on the organ.
At the hospital, Mariko's health shows a marked improvement but at night she begins to scream, demanding the removal of something from her body; her caretakers dismiss her demands as nightmares.
In his lab, Nagashima finds the liver samples growing at an exponential rate. One night, a gelatin from the liver mixes with samples from a bottle labeled "Eve" and possesses the lab assistant Sachiko. Later that night, Nagashima enters the lab and finds a gelatinous form that morphs itself into the form of Kiyomi. Nagashima approaches her, and they embrace and have sex on the lab floor. Afterwards, the being resembling Kiyomi deteriorates, leaving Nagashima alone.
At home, Nagashima finds Kiyomi's journals, which reveal she was losing control of herself and hearing voices that made her attracted to Nagashima's work, and to manipulate her actions to get Nagashima to perform his experiments, leading up to the previous night. Sachiko approaches Nagashima and tells him to attend her presentation at a science conference. At the conference, Nagashima meets with Yoshizumi, who says Mariko has grown stranger each day and that even her uterus is changing. Sachiko begins to present, revealing herself to be a mitochondria collective that will replace humans and can control the mitochondria in humans. The creature says they have found an ideal womb in which to continue their process. Nagashima asks whether the creature is Eve, before it causes a man in the audience to burst into flames through the mitochondria in his body, which leaves the audience in a panic. Nagashima tells the doctor the creature has collected sperm and is looking for a womb in which to cultivate it, and they both rush to the hospital.
At the hospital, Mariko's abdomen convulses wildly as staff try to help. When Nagashima and Yoshizumi arrive, they find Mariko has fainted and the creature is attempting to escape with her. The creature slowly leaves while setting people on fire as she moves through the hallways. Nagashima and Yoshizumi attempt to use security doors to prevent the creature from escaping, so she moves to the roof with Mariko. Nagashima pleads with the creature, calling her Kiyomi, to let Mariko go. The creature responds her form is a new evolution, that Mariko will bear the real Mitochondrial Eve, and that the mitochondria controlled all events in Kiyomi's life that led to this point, including manipulating her to fall in love with Nagashima. Nagashima calls out to Kiyomi as the creature tells him to go away and sets his arms on fire. Nagashima continues forwards and embraces Kiyomi, and they both erupt into flames. Takashi arrives on the roof and rescues Mariko as the creature and Nagashima continue to burn.
