A scientist by the name of Shiragami is driven insane due to the death of his only daughter Erica. At the brink of madness, the scientist begins to experiment with biotechnology and is able to successfully combine the DNA of a fish with that of a mammal to create Deutalios, a 50 meter creature that resembles a rat. It's not long after its creation that the beast is found terrorizing Yokohama, attracting the attention of Godzilla who arrives to confront the monster. The two titans engage in combat, but Godzilla quickly gains the upper hand on his smaller opponent and kills the creature. With his foe dead, Godzilla begins to eat the remains of Deutalios.

Meanwhile, Doctor Shiragami continues with his experiments, this time managing to create a hideous creation that he dubs Biollante. However, a female reporter, who is trying to discover the origin behind Deutalios, winds up near Shiragami's lab before she starts to have a physic vision of a group of humanoid flowers chanting her name. The reporter then meets with Shiragami where she relates her vision, prompting the doctor to confess that he had been tampering with the DNA of a tropical plant and that of his deceased daughter, which is what lead to the birth of Biollante.

Eventually, Godzilla appears again and Biollante leaves the vicinity by burrowing underground toward the nuclear leviathan, emerging next to its opponent. Biollante uses its radioactive sap spray on the King of the Monsters, which badly burns Godzilla and forces him to retreat into the sea. Shortly afterwards, though, Biollante is consumed by a cloud of smoke as her mutation goes out of control.

This was the original script for the film Godzilla vs. Biollante (1989). Reportedly, Toho held a story contest in 1985 for the next installment of the Heisei series, tentaveily dubbed Godzilla 2, and the winner was Shinichiro Kobayashi, a dentist, who created this early draft for Godzilla vs. Biollante. The original story, which was created on June 10th of 1985, was very different from what would evolve into Kazuki Omori's final script though. What little did survive includes: the death of Erica, her father being the creator of Biollante through her DNA, a psychic girl and, for the most part, the climax.

After going over the winning entry, producer Tomoyuki Tanaka and Omori felt that Godzilla was not focused on enough in the story. So the concept was changed heavily to focus instead on Godzilla rampaging across Japan for a majority of the movie. Elements from another script in the contest, which involved utilizing Godzilla's cells, where also incorporated as it became an important subplot to the movie as the Self Defense Force now had the objective of creating and utilizing the ANEB. It was also decided that the Super-X concept would be continued for the feature, as a second version of the craft would appear.

Omori's new vision for the production also called for the axing of the Deutalios creature, and in its place creating an earlier form of Biollante that closely resembled a rose. The psychic elements hinted at in Kobayashi's initial concept were also focused on much more in the final screenplay, as the movie would introduce the character Miki Saegusa and her school of "gifted" pupils. Interestingly to note, in Omori's original screenplay, Miki was intended to lift Godzilla, using telekinesis, during their confrontation; however, this idea was removed as Tanaka was extremely opposed to the concept.

In terms of history, contest winner Kobayashi ended up creating three different drafts around the idea, the last of which was submitted on January 30th of 1986. From there, Omori submitted his first screenplay on October 1st, 1986, titled Godzilla 2. This was also reworked the following year in two more screenplays, one titled Godzilla II - Godzilla 2 (the first part in English) and the other titled Godzilla II - Godzilla 2: Godzilla vs. Biollante. In 1988, producer Shogo Tomiyama drafted up a new proposal for the film called Godzilla: Godzilla vs. Biollante, for which little is known about but ultimately the company went with a fourth and then a fifth and final revision by Omori that were submitted in July of 1989.

As a side note, the four-part mouth design for Biollante above was one created by designer Shinji Nishikawa when originally doing concepts for the monster's final form and this design was then approved by Koichi Kawakita. However, it did not make it into the final film as the producers ended up wanting a more reptilian-like look for the creature.