Kōichi Doi develops nutritional solutions for Defy Foods, specializing in food formulations designed to preserve astronaut bone mass in the International Space Station's zero-gravity environment. His work produces functional but unappealing space food consumed by the crew, including Orudo Noguchi.

During a routine medical check revealing abnormal bone volume increases and radiation symptoms in Noguchi and another astronaut, Doi voices concern about potential links to his food formulations, hinting at safety issues. He accepts Noguchi's personal request to deliver a small package to the astronaut's daughter, Monaka, on Earth.

After the astronauts mutate into violent, bone-armored monsters due to an interaction between his inadequately tested food and space radiation, Doi escapes the chaos via an emergency pod. Defy Foods, aiming to suppress evidence of corporate negligence, dispatches agents to contain the situation. These agents confront Doi and a surviving doctor, coercing their silence about the incident. While Doi protests his innocence regarding the mutations, he complies with the company's directives.

Accompanying the agents during the monster's rampage on Earth, Doi witnesses Monaka battling the creature. Once the monster is temporarily incapacitated, he identifies it as Noguchi and reveals Monaka's connection to it. When Defy Foods agents attempt to eliminate Monaka to tie up loose ends, she kills them first. Cornered and exposed, Doi is then executed by Monaka.