Stolen Starseed Senshi
The senshi of our solar system were shocked when they discovered there were senshi throughout the Galaxy, not just themselves. The members of the Shadow Galactica (those who worked for Galaxia) were sent to assassinate these "other" senshi. (This is from the manga) Galaxia promised them that if they killed their assigned senshi, they would obtain their powers. We only know that Lead Crow and Tin Nyanko acquired their powers this way; for the other members of the Shadow Galactica, you have to assume they either a) stole starseeds to obtain powers; or b) were really senshi in the first place, but recieved the bracelets from Galaxia after she stole their starseeds. Confused? You better read the Sailor Stars Summary!
Here is a list of the original senshi's name and arrows pointing to who they became or who stole their powers.
Sailor Mau (the planet Luna and Artemis are from)>>>>>>>>>>>>>>>>>>>>Sailor Tin Nyanko
Sailor Chuu>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Sailor Iron Mouse
Sailor Mermaid>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Sailor Aluminum Siren
Sailor Coronis (the planet Phobos and Deimos are from) >>>>>>>>>>>>>>>Sailor Lead Crow
Sailor Cocoon (only in the manga)>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Sailor Heavy Metal Papillon