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a person trained in ancient Japanese martial arts and employed especially for espionage and assassinations to watch other Ninjas secretly usually for hostile purposes.

Generally more trained than the traditional Ninja, unseen by the careful eye of a Ninja. Can be seen as a more elite ninja.
David was certain he was unseen to the naked eye as a Ninja in the night, but little did he know that he was being tracked by a Ninja Spy.
by mad_cat October 21, 2010
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