hile enjoying the flower gardens, Sailor Moon (Usagi) and friends encounter an old childhood friend of Mamoru's: an alien! He's come back to give Mamoru a special flower, but doesn't like Usagi and the rest of the planet's inhabitants. Sailor Moon must defend the earth from the evil Kisenian Flower he's brought back... before the evil vines and blossoms overrun the planet!

Overview from themoviedb.org