Kagero is amoung rare kind of Ninjas serving that she is a woman. She spent her years as her Grandfather’s pupil until he was killed by her major enemy, the Kawagami. She fought with Tsimbaro a trusted friend until he disappeered. She now is a Ninja Wanderer following where her feet take her.
The local band of 'nasties' (goblins / orcs / whatever) lives in relative peace with the local population.
Along come the PCs and go through their usual heroic monster bashing routine, wiping out the nasties and pinching all their stuff, then continue on their way.
Problem is, they don't kill ALL he nasties. The survivors want revenge and, after spending a few months recovering, start to take it in their own inimitable style (which is not unlike that of the PCs come to think of it).
Next time the PCs are in the area they find themselves VERY unpopular with the townsfolk.