Iwao Himuro serves as the primary antagonist of the film, where he is the director of the Institute of Super Science, abbreviated as ISS. This organization is presented as the Japanese branch of a vast and shadowy global corporate syndicate known as the Foundation. On the surface, Himuro presents himself as a refined and kind gentleman, but this facade conceals a truly ruthless and heartless nature. He is a deeply paranoid and uncaring individual who views the people under his employ not as human beings but as disposable assets and potential products to be exploited for profit.

Himuro's primary motivation is the production of cybernetic soldiers to be sold as guerrilla combat units, a venture he sees as having immense economic value. To achieve this, his organization uses the pretense of finding cures for terminal illnesses like cancer and AIDS to recruit promising scientists. This is how Daimon Kazamatsuri, a specialist in clinical immunoengineering, and his colleague Giichi Onizuka are brought into the project to research human cell remodeling. Himuro's interest in their work is purely transactional; he is impressed by Onizuka's studies on grasshoppers only insofar as they can be applied to his military ambitions.

In the story, Himuro's role is to be the cold, calculating force of corporate evil that sets the tragic events in motion. He maintains control over the research by manipulating scientists like Daimon, often using veiled threats and coercion to ensure their compliance. His paranoia leads him to believe Onizuka is a spy, and after a confrontation, he has the scientist imprisoned and then fired from the project, ultimately ordering him to be disposed of as little more than a product sample. When Onizuka is seemingly killed, Himuro simply shifts his focus, using Daimon's son, Shin Kazamatsuri, as leverage to force the father's continued cooperation. Himuro's key relationships are therefore defined by exploitation and control. He has a manipulative hold over Daimon, a purely antagonistic view of Shin as a valuable specimen to be reclaimed, and a contemptuous attitude toward Onizuka, whom he mocks and discards.

The character's development throughout the narrative is a progression from a position of total control to a state of desperate, cornered rage. He initially operates from the safety of his position of power, dictating the fates of everyone involved. However, his plans begin to unravel when the ISS comes under a devastating physical attack from a battalion squad. Following this assault, Himuro is severely chastised by the Foundation's headquarters for the failure, leaving him with nothing left to lose. In a final act of desperation, he tries to personally eliminate the surviving members of the Kazamatsuri family. Armed with a submachine gun, he aims at Shin. It is in this moment that Shin's pregnant girlfriend, Ai Asuka, takes the fatal bullets meant for Shin, an act that directly leads to Himuro's demise. In a fit of rage and grief, Shin transforms and brutally kills Himuro, bringing an end to the villain's reign of terror. Himuro himself possesses no superhuman abilities; his power lies entirely in his position, his manipulation, and the lethal force he is willing to use, such as his submachine gun, to eliminate anyone he considers a threat or an obstacle.