Only the staunchest Pirate fanboy can deny that Ninja have some level of awesome. Any story that can reasonably fit Ninja in there, like stories in Feudal Japan, or the fantasy equivalent, will do so. Sometimes, those fantasy equivalents seem to exist solely to give them a reason to include the Ninja.
Then again, some stories can't easily fit them, but throw them in anyway. It doesn't have to [...] [tvtropes.org]