Shin Kazamatsuri, a professional motorcycle racer, wakes from a recurring nightmare of a monstrous grasshopper-like creature committing brutal murders, only to realize the dream is a telepathic echo of a real-world horror. He has volunteered as the primary test subject for a cutting-edge genetic research project led by his father, Dr. Daimon Kazamatsuri, and his partner, Dr. Giichi Onizuka. The public goal of the research, conducted at the Institute of Super Science, is to find cures for diseases like cancer and AIDS by unlocking the potential of the human body. Unbeknownst to Shin and his father, their work is funded by a powerful criminal syndicate that intends to weaponize the research to create a new breed of unstoppable cyborg soldiers.

Shin soon discovers that his body is undergoing a terrifying and involuntary metamorphosis, granting him phenomenal strength and agility but also transforming him into a humanoid grasshopper hybrid designated as a Level 3 augmented soldier. He finds himself caught in a crossfire of sinister agendas. The syndicate, led by the ruthless Iwao Himuro, views Shin as an unstable and dangerous asset to be eliminated. At the same time, Dr. Onizuka has secretly pursued his own megalomaniacal vision. Rather than creating mere soldiers, Onizuka seeks to evolve humanity by fusing insect DNA with his subjects, aspiring to become the god of a new species. He has already performed the experiment on himself, becoming a feral, monstrous grasshopper creature who is the true perpetrator of the murders plaguing Shin’s nightmares. Their shared grasshopper DNA creates a telepathic link, forcing Shin to witness Onizuka's gruesome rampages.

As the conspiracy closes in, Shin must protect those he loves. His girlfriend, Ai Asuka, a nurse at the institute who is pregnant with his child, becomes a primary target for the syndicate. After revealing the truth about the experiments to Shin, she is gunned down by Himuro. With her dying breath, she begs Shin to protect their unborn child, who has inherited his mutation and is also being hunted. Consumed by rage and grief, Shin fully embraces his monstrous power for the first time. He confronts Himuro and his henchman, Goushima, an older-model cyborg soldier. Shin kills them both in a brutal confrontation, destroying the institute's leadership. Meanwhile, the CIA, through agent Sarah Fukamachi, has been monitoring the situation. They ultimately corner Dr. Onizuka, setting him ablaze. As he burns, Onizuka sends a final telepathic plea for help to Shin, who can only watch as his creator and tormentor is consumed. Left alone, transformed, and hunted by both the syndicate and the government, Shin Kazamatsuri disappears into the night, a tragic hero burdened with a monstrous form, a world that sees him as a threat, and the desperate promise to protect the new life he and Ai created.