Akae Masayuki is a sniper for a national anti-terrorism special force team know as ZAT (Zap Assault Team). During a criminal hostage-taking raid on a bank, due to a sniper mistake, a gunfight breaks out between ZAT and the criminal gang. During the raid, ZAT captain Hisakawa Takerou loses his right arm which Masayuki blames himself for and ends up quitting ZAT. Hisakawa, who's worried about Masayuki, decides to visit and asks him if he would like to work as a "killer." On his first day of work, he finds out that his former best friend, Shimada Shuuji, is also working as a killer, but his target is none other than Masayuki himself. Thus begins a dangerous journey as Masayuki tries to figure out what happened between him and Shuuji that makes his former best friend want to eradicate him from the face of the earth.