Aya, Youji, Ken, and Omi are the four young men who comprise Weiss Kruez (WK), an assassin group who eliminates certain menaces to society. Each member has his own trademark fighting style. Aya is adept at fighting with a katana, Youji has mastered the art of strangulation via strings, Ken is lethal with his metal claws, while Omi specializes in a wide array of projectiles. Under the command of a mysterious man known only as "Persia", the WK is dispatched to take care of drug rings, terrorist factions, and the like. But as things go along, they discover that most, if not all, the bad elements they have dealt with are somehow connected to the Takatori family. The Takatori family is rich, powerful, and influential. It seems if the problem is to be nipped in the bud, the WK would have to put an end to one of Japan's most prominent clans.

Koua is an academy that brings Japanese's most talented people and students together. The mission is to train talented people to bear the world's future leadership. However, recently, the suicide rate in the academy is increasing and there is hardly any information being released to the public. Fujimiya Aya is sent to inflitrate this school carrying out criminal investigation and disguise himself as a teacher. In fact, actually, there is a connection between Koua academy and the global terrorist activities that are frequently occur. Therefore Persia assigns Hidaka Ken and Kudou Youji as well into this mission to solve the truth and connection of the incident behind Koua academy.