Koga Ninja

Koga Ninja were a ronin "clan" that defended the lower classes against samurai excesses.

Koga
In the early days of the Empire the peasants of the village of Koga were terribly abused by the samurai who oversaw their taxes. When he defiled the village hetman's daughter, several of the village men attacked and slew him while he was drunk. When other samurai came, the villagers blamed the death on mysterious shadow warriors who struck in the night. Since this day the so-called Koga Ninja were borne.

Championing the Weak
Koga was destroyed during the Clan War, and the Koga ninja had long since abandoned the village as the base of their operations. They had spread throughout Rokugan, protecting the lower classes from the predations of the samurai class.