Biollante is a film rebooting Biollante's story, although Godzilla is not in it at all. The film only features Biollante, and the sequel is supposed to feature a battle between Biollante and Godzilla.
A scientist tries to bring back his dead daughter Rose by using cells from a special plant that regenerates when harmed. He uses a sample of her blood from when she was alive, and uses it. While he's at home, however, a lab rat in his laboratory gets loose and accidentally knocks over a shelf of chemicals that fall down into the serum and mess it up. The scientist discovers this when he finds a strange sentient plant growing in his lab.
He begins to come to terms with the fact that this mutant is his daughter, and he starts to care for it, but as he feeds and takes care of it it begins to grow into a humanoid vegetation monster that rampages throught he lab devouring all sorts of chemicals until it grows giant. The monster attacks the city in search of more food, and when the scientist finds out he has a nervous breakdown.
In the end, the monster is shot down and drained of all it's nuclear energy until it shrinks down and begins to die. The scientist holds the poor creature in his hands and begins to cry as he sees his daughter die once again.