After a terrorist bombing takes the life of his only daughter, renowned bio-geneticist Professor Shinigami merges her cells with those of her favorite rose in life. When the rose is almost destroyed in an earthquake, he also bonds Godzilla cells, which the Japanese government gathered for study after The King Of The Monsters last raid on Japan, to the plant to make it immortal.
The same terrorists want the G-cells, and threaten to unleash Godzilla once more if the Japanese government fails to give in to their demands.
Soon, Godzilla returns and makes his way towards the genetically altered plant, which has now mutated into the colossal horror called Biollante!