The Ninjas struck from the shadows in the BR 1,999, routing the Bat Knights that held sway at the moment. The Ninjas brought with them a lethal weapon known as a katana, whose terrifying power would make the enemy halt and go "Katanas are totally awesome!" instead of defending themselves from said weapon.
Ninjas enjoy makeing new types of weapons which are only effective when used by other ninjas. One example of this is the throwing star, which while in many ninja movies is quite deadly, In real life it is unlikely to even give somebody more than a minor laceration. How this is accomplished is currently unknown. Some ninjas have taken this skill tho the extreme, useing doughnuts or cookies as throwing stars and still manageing to pown all in thier path
The nemesis of the Ninjas are the Pirates. These two factions hold a terrible hatred for each other, and constantly battle to prove which side is more awesome. As with pirates, there are generally two types of Ninjas -- regular ones and Space Ninjas.
Space Ninjas are like regular ones, except they have better teknology and weapons. They travel the stars doing Space versions of whatever ninjas normally do. You know, like Space-assassinating people and getting Space-involved in the Space-drug trade. No one knows where their homeworld is or why they kill certain people or what their motives are. All that's known is that most people love them since they usually bring chaos and terror wherever they go.