Piercing through the immeasurable distances of the cold vacuum of space, a massive meteor collided with the Earth just outside of Sapporo. When the military arrived, no trace of the object remained. The mystery thickened as electronic interference plagued the South side of Sapporo, and fiber optic cables seemed to vanish into thin air. Suddenly, a brewery was attacked, and at the scene of the incident, silica residue was discovered. When things seemed as though they couldn't possibly get worse, the creatures responsible for these anomalous events staged an attack on a subway train. The Symbiotic Legions, as they were called, were making their deadly presence known.

Killing anyone unfortunate enough to stand in their way, the Legions continued to process any trace of silica they could find in order to feed oxygen into their flower. Once the flower blossomed into maturity, it would launch an ominous seed and spread more vile Legions into far reaches of space. The Self-Defense Force was forced to respond tot he growing threat, but the military became increasingly wary of the oxygen-rich environment in Sapporo. C-4 was planted at the roots of the flower, but the resulting explosions were of little effect. Luckily, Gamera finally arrived on the scene, destroying the plantlike organism with the burning blaze of his plasma fireballs. In response to the death of their organic reproductive center, the Symbiotic Legions launched an offensive against the creature responsible. Clawing and piercing into the towering turtle's hide, the sadistic creatures attempted to tear Gamera's flesh to shreds! Shortly after the attack commenced, the hive became mysteriously attracted to a nearby transformer, where they were eliminated by the searing electricity. With his enemies defeated, Gamera rocketed into the sky. The Legions, meanwhile, retreated to Sendai, where a giant queen Legion now roamed. Gamera attempted to repel the monster; however, it was severely weakened in the process. The situation was dire, for a nearby Legion Flower launch its seed. Throwing his body on the Legion Flower, Gamera prevented the pod from leaving the ground. In the process however, Sendai was destroyed.

The Legion queen began to set a path for Tokyo, and fought her way through the military resistance with her sinister swarm of Symbiotic Legions. Gamera, badly burned from the explosion in Sendai, was finally rejuvenated and rushed to reenter the fray. The swarm was sent to attack Gamera once more, but a nearby power plant activated its power just in time. The Symbiotic Legions attached themselves to the transformer, and a nearby soldier fired a flare to signal for air support. Helicopters aimed at the insect-like aliens and completely ended the Symbiotic threat, forcing the queen to fend for herself...