Within Thailand, there is Roanapur, a filthy, crime-ridden city where not even the authorities or churches are safe from the grasp of corruption. The city is infamous for being the heart of illicit activities and operations, typically supported by local criminal syndicates. It is a shelter for prisoners and degenerates alike. Enter Rokurou Okajima, an ordinary Japanese businessman who has been leading a dull and repetitive existence until he gets his chance for a change of pace with a delivery trip to Southeast Asia. His business trip quickly takes a turn for the worst when Rokurou is kidnapped by Black Lagoon, a mercenary outfit operating in Roanapur. The organization intends to use him as a bargaining tool in failing discussions. His old employer has now abandoned and deceived him.