Eclipse 03

The vine is just the start.  The gas being emitted by the facepiece is keeping the heroine drowsy, but it is also giving her specific chemicals.  Chemicals to prepare her womb for seeding, and her breasts for milking.  As the plant grows, it will move her legs apart, and begin to pollinate her over and over.  As the motile seeds emerge from her pussy (each one giving her an orgasm), they will move up to her breasts to feed.

The heroine will be the seed mother for a generation of plants that will be used to take over the city (or just capture other heroines to keep on breeding).  Cloning the heroine to make planet-women would also work, so the villain has minions.