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.