The Crescent Mask

From the publisher:

In the shadowed valleys of Kurogane, a sinister tale unfolds. The land trembles under the threat of an unseen predator—a murderous ninja whose deeds are whispered of in terror. As the bodies pile up, so too do suspicions, driving ancient rivalries into violent action. This is a land caught in the grip of vengeance and fear, where the blade sings not for honor, but for slaughter.