After Godzilla's return in 1984, the city of Tokyo, Japan had suffered a great deal of destruction. During the aftermath and cleanup, forensic workers collected small remains of skin from Godzilla, which were later transported to a government lab facility in the arid wasteland of Saradia. A scientist by the name of Dr. Genshiro Shiragami intended to use the genetic material of the Godzilla cells in the skin to genetically enhance various species of plants to create crops resistant to harsh weather and unfavorable conditions of Saradia. Unfortunately, numerous other nations did not approve of this move in agricultural wealth-as Saradia relied on exports for its produce-and an act of terrorism was put into plan to bomb the laboratory working with the cells. Amongst the scientists who lost their lives was Erika Shiragami, Dr. Shiragami's daughter. Her loss was terrible to him, and he proceeded to collect DNA from his daughter and splice it with that of a rosebush in hopes of preserving his daughter's spiritual entity. Five years later, in 1989, an earthquake destroyed the roses' shelter, thereby killing several. Dr. Shiragami panicked, and carried out a risky and unauthorized plan to splice the Godzilla DNA with a lone rose, in hopes that the rose would remain alive and hopefully invincible. However, the seemingly successful fusion of the cells resulted in the slow but eventual growth and mutation of the rose, which eventually became capable of thinking and moving, and eventually proceeded to smash its way through the laboratory wall, making its way to Lake Ashino, where it rooted itself and took up residence.
Biollante's first encounter with Godzilla was inevitable. Godzilla had actually sensed the presence of another living being with the same genetic makeup as himself, and felt an uncontrollable urge to travel to the originating site of this feeling. It was also mentioned by Miki Saegusa, an individual endowed with ESP, that Biollante had been "calling out to Godzilla" (whether or not this calling was intentional or not was never explained). Biollante, in her first encounter, fought defensively with wave after wave of tangling vines. Despite the great effort that the plant/monster hybrid exerted, it failed miserably and took heavy damage from Godzilla's atomic beam. Godzilla eventually managed to set Biollante aflame as Biollante seemingly burned to death. However, it was reaffirmed that Biollante was immortal as everyone watched Biollante begin dissolving into energy particles to ascend into space.
Later on, Biollante confronted Godzilla again, this time at her own will. Their second battle had clearly turned the offensive/defensive tables. Biollante was clearly pursuing and fighting Godzilla offensively, to eliminate his threat to the inhabitants of Earth. Whereas, Godzilla was now fighting with all his might to defend himself against such a colossus who fought just as mercilessly as the King of the Monsters himself. The outcome of the battle resulted in Godzilla winning, but having to return to the ocean as the Anti-Nuclear Energy Bacteria began to take effect, slowly weakening him. He clumsily lumbered to the coast, collapsing into the sea face first, lying apparently unconscious. Biollante, mortally injured from the battle, dissolved into spores that ascended into the sky, apparently dying. Shortly after, Godzilla regained strength from the cooling waters of the ocean (which stopped the breeding of the bacteria). Exhausted from his battle and illness, Godzilla headed out to sea to recuperate.
At first, Biollante was a giant rose with teeth inside her bud and long vines (merely a heavily-mutated and exceptionally large "thinking" rose). In her second form, the Godzilla genes took over and Biollante's body became an abomination of biological science. Biollante's second form had a head like a mosasaur's and a jaw with knife-like teeth, even on the interior lining of her mouth. In addition, six large tusks (three on each side of her mouth) protruded from the fulcrum-region of her mouth. Large numbers of vines and tendrils were a primary feature of Biollante. Some vines ended in sharp, spear-like ends, while others sported small, sharp-toothed mouths. In Biollante's first form, a large, fleshy sac was surrounded by her overlying vines. In her second form, what appeared to be meaty flesh was seen underneath the tangled mess of vines and plant-tissue. The fleshy surface was pink and had many wrinkles and lines, resembling a brain-like surface.
Biollante, in her rose form, could constrict and grapple with an enemy through the use of numerous vines, some of which ended with fanged mouths that not only were able to bite an opponent but were capable of spitting a highly corrosive acid sap that could blind an opponent. If severely injured, Biollante could dissolve into golden energy spores and ascend into space for recovery. In Biollante's rose form, her cellular division was shown to be abnormally affected by Godzilla's atomic beam, resulting in heavy bodily damage. Biollante's second form was displayed as a horrible plant abomination sporting a massive jawed head with countless teeth and enormous tusks; an arched back with plate-like plant spines; and four stubby, root-like legs that Biollante utilized as a means of locomotion. Biollante retained all former abilities as well as gaining the ability to release large quantities of radioactive corrosive sap from the mouth. Several of her vines also ended in thorny spears which were capable of penetrating even Godzilla's flesh. Despite her plant-like body and rather unwieldy appearance, Biollante was capable of moving across the ground rather quickly.