Fiore is the secondary antagonist of the "Sailor Moon R" movie (known as "The Promise of the Rose" in the English dub). He is an alien and childhood friend of Mamoru (Darien) when the latter was orphaned.
Fiore's name means "flower" in Italian, though despite his name being spelled in singular form, it is pronounced like the plural "fiori".
Fiore was drifting alone in space in childhood before he had come to the orphanage where Mamoru was raised. One day, when Mamoru had given him a rose, Fiore vanished (due to the Earth's atmosphere not being appropriate for him) promising to get flowers for him. When he went to another planet, he tried picking the best flower possible, but when he picked the Xenian Flower, he'd turned to the dark side and he'd been evil ever since.
Although Fiore tried to get rid of Sailor Moon and the other Scouts, Sailor Moon returned him to the light with a story of how Mamoru had become her friend when they were children. This was after Fiore had left. At this point, she got roses for her mother, who had already born a son at the time, and she gave him one. Because of this past, and because her moon crystal had turned into a flower, he hesitated to take the crystal, and the Xenian flower vanished in wrath.
After Sailor Moon dies, a reformed Fiore keeps his promise by giving Tuxedo Mask (Mamoru's alter ego) "his life", which was (as he said, returning to his juvenile form) the friendship flower full of life energy. After Tuxedo Mask puts its nectar on his lips and kisses Sailor Moon, she is resurrected, and Fiore leaves, this time by bubble, as before he had even arrived at the orphanage.
Remains of the Film
It is shown that Fiore would hit and push a girl, as when Usagi (Serena) was trying to get Mamoru's attention, Fiore pushed her down, especially because he thought she was trying to keep him from keeping his promise.
(More to be announced.)