Okajima Rokuro is a Japanese businessman…in a town full of Japanese businessmen. His normal day consists of social drinking with clients and being kicked around by his bosses. He finally gets a break though, as he’s sent by his company to the tropical seas of Eastern China to deliver a disc…only his boat gets hijacked by a band of mercenaries that were hired to steal it. “Rock” (as he is newly dubbed by his captors) catches the interest of the only female merc “Revy” as she thinks he’s worth a ransom, taking him hostage. However, the disc turns out to be more trouble than its worth, and complicates things both for Rock, and the mercenaries known as Black Lagoon.
Godō Kusanagi is a 16-year-old high school boy, who once killed the god "Verethragna" and acquired the title of "Campione" ("God Killer") when he was 15. Erica Brandelli is a 16-year-old Italian girl, who is a "Great Knight" of the magic society "Bronze Black Cross" and had fought together with Godo to defeat Verethragna. Godo doesn't like fighting but his title of "Campione" makes him get involved in battles against other Campiones and uncontrollable gods.