Shiba, a detective in the fifth anti-organized crime division of the Tokyo Metropolitan Police, a.k.a. "Anti-Gang 5," is on the handgun smuggling beat. A so-called handgun confiscation specialist, the most important element of his investigations is the information gathering skills of his undercover informant S. Shiba's "S," Munechika, also happens to be a big-time yakuza. Though he was aware of the special feelings he had for Munechika, Shiba chose the life of a detective. Thinking of each other, they swear to protect their relationship as S and detective. But then one day, a mysterious young man named Black appears before Shiba, and everything falls apart!