Long before Mamoru found his destiny with Usagi, he gave a single rose in thanks to a lonely boy who helped him recover from the crash that claimed his parents. This long-forgotten friend, Fiore, has been searching the galaxy for a flower worthy of that sweet gesture long ago. The mysterious flower he finds is beautiful, but has a dark side- it has the power to take over planets. To make matters worse, the strange plant is tied to an ominous new asteroid near Earth! Faced with an enemy blooming out of control, It's up to Sailor Moon and the Sailor Guardians to band together, stop the impending destruction and save Mamoru!

A strange new flu is causing everyone in town to get sick, including the Sailor Guardians. Minako is the only one still healthy and takes it upon herself to look after her sick friends.