Flau was a Youma summoned by Jadeite to drain energy from unsuspecting radio-listeners as part of the Dark Kingdom's continuing energy-gathering efforts. She appeared in anime episode 3.
She and Jadeite hijacked FM No. 10 and broadcasted the new program Midnight Zero. Midnight Zero was a program that would read one love letter per night from the fan mail; the fan whose letter was read won a flower pin that would be delivered to them the next morning. These flowers, however, would then sap the energy from whoever was wearing it at the time. Usagi's friend Naru, as well as their teacher, Ms. Haruna, fell victim to these energy-draining flowers, and both eventually fell into comas.
Once Usagi disguised herself and stormed into the broadcast station to protest, Flau lunged through the sound-proof glass and attacked her, transforming from her human disguise into her true form, a humanoid female with pale blue/purple skin, a blue toga, and unruly brown hair, with a dark star on her forehead. Usagi then transformed into Sailor Moon and was chased by Flau to the roof of the building, as the Youma attacked her with blasts of energy from her mouth and swipes of her sharpened claws. Sailor Moon then used her tiara to try to defeat Flau, but missed. She then drew it back, and it sliced through Flau and defeating her. http://www.wikimoon.org/index.php?title=Flau