Sylvie is a female character who appears on episode 5 "Moonlight Rambler". She and her friend Anri escape and crash-land near Megatokyo. Upon reaching the metropolis, Sylvie befriends Priss without revealing her origin. It is revealed that she is a Sexaroid (a Boomer designed to be a love-doll) model 33-S designed to feed on human blood and pilot "D.D.", a heavily-armed mecha with a fail-safe mechanism that can set to self-destruct if the pilot's vital signs reach flatline. Priss is left no choice but to kill Sylvie to deactivate the D.D.'s self-destruct mechanism.

In the near future, Tokyo was left flattened as a result from a great earthquake. A new city, MegaTokyo, was then recreated due in no small part from the aid of a multi-million dollar company, Genom Corp. Genom created and mass-produced biomechanical creatures called Boomers to aid in the restoration of MegaTokyo. When the Boomers began to run out of control, the ADPolice at first tried to stop them, but they proved to be far more difficult to deal with than was first imagined. Under the ever looming Boomer threat, a group of four girls from varying degrees of society banded together. Calling themselves The Knight Sabers, they were the only ones with enough firepower and resourcefulness to defend the fledgling MegaTokyo from Genom and it's berserk Boomers.
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(Source: Anime News Network)