In PARASITE WAR, Ota stars as Sachiko Obayashi, an investigator for the Ministry of Health, Labor, and Welfare who crosses paths with a malignant extraterrestrial organism known as a "Mule". The "Mule" attaches itself to the inside of its victim's skull, manipulating the body like a puppet before ultimately devouring the brain. When hiding in a human host, the "Mule" is virtually indistinguishable from a non-infected person.
Obayashi tracks the parasite to read morea hospital, where she manages to trap it in a secluded wing. However, the "Mule" immediately abandons its injured host body and finds a new host. Sachiko most discover who is infected from a group of 5 people - a doctor, a nurse, and three patients - before the "Mule" manages to escape.