Sylvie is a female character who appears on Moonlight Rambler. She and her friend Anri escape from the space station Genaros and crash-land near Megatokyo. During the escape, Anri was badly injured, leading Sylvie to murder people and steal their blood to keep Anri alive. 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 which was inexplicably designed to feed on human blood. She is also the pilot of "D.D.", a heavily-armed mecha with a fail-safe mechanism that can set to self-destruct with a nuclear reactor if the power runs out. Priss is left with no choice but to kill Sylvie to deactivate the D.D.'s self-destruct mechanism.
Sylvie is voiced by Yoshino Takamori in Japanese and Martha Ellen Senseney in English.