From Anime News Network:
In Korea in 668 AD, North Star, using the martial arts discipline of Sashinmu, went into a beserker rage and massacred 100 of the most skilled martial artists of his time. After the massacre North Star and the lethal art of Sashinmu disappeared.
Now it is 20 years later and a text of Shashinmu has surfaced again. A mysterious cadre will do anything to gets its hand on it and learn the deadly art. Meanwhile it is up to the book's protectors, Rin Yhun and Bi-ryu, to destroy it before the forces of evil get their hands on it. But should the secrets of Sashinmu be destroyed forever? Or should the art be mastered and used by the book's protectors?