Aya, Yoji, Ken, and Omi are the four young men who make up Weiss Kruez (WK), an assassin gang that kills societal threats. Each member has a distinct fighting style. Aya is skilled with a sword, Yoji has mastered string strangling, Ken is deadly with his metal claws, and Omi excels in a wide range of munitions. The WK is assigned to deal with drug gangs, terrorist factions, and the like, under the supervision of a strange figure known only as "Persia." However, as time passes, they realize that most, if not all, of the negative forces they have encountered are linked to the Takatori family in some way. Takatori is a wealthy, powerful, and important family.