Trying to Remember name of a Particular Anime

About a year and a half ago I remember seeing this Ninja anime, where the lead was this female assasin who used sex as a way of getting close enough to her targets to kill them. It was not a hentai though, but a rather gory anime. Any ideas? or any names?

after some more research, i finally found it. The name of the anime was "shadow" OAV. Theres only 4 episodes but it seems episodes 3 and 4 never got subbed