Rokurou "Rock" Okajima has joined the Lagoon Company, a pirate mercenary group which operates out of Roanapur, Thailand. Despite his initial protests, this filthy slum of depraved souls and merciless criminals now serves as the former salaryman's home. Stranded, with nothing left of his past life but the clothes on his back and his inner morality, Rock is forced to perform jobs alongside the other members of the Lagoon crew. Berated for his lack of spine as he wades through the underbelly of society, he must decide whether to continue on amidst the gunfire and ruthlessness or risk everything he has in an attempt to be free. Whether he chooses the comfort of a familiar land or the freedom of being an outlaw, his decision will have lasting consequences on the crew who gave him a home.

Roberta, the terrorist-turned-maid that made her appearence in the first season of Black Lagoon, returns in this five-episode OVA series—and this time, all bets are off! Roberta's benefactor, the patriarch of the Lovelace clan, is murdered during a political rally. The assassin's trail soon leads back to Roanapur—so now she has returned on a mission of vengeance! However, close behind her is the new patriarch, Garcia, as well as Roberta's apprentice (and maid), Fabiola Iglesias. As the body count of Roberta's bloody rampage mounts, forces from within the corrupt island (which includes the Lagoon Company), as well as overseas converge on what threatens to escalate into all-out war!

Losing a loved one is so painful that one may sometimes wish to be able to resurrect them—a weakness that the enigmatic Millennium Earl exploits. To make his mechanical weapons known as "Akuma," he uses the souls of the dead that are called back. Once a soul is placed in an Akuma, it is trapped forever, and the only way to save them is to exorcise them from their vessel using the Anti-Akuma weapon, "Innocence." After spending three years as the disciple of General Cross, Allen Walker is sent to the Black Order—an organization comprised of those willing to fight Akuma and the Millennium Earl—to become an official Exorcist. With an arm as his Innocence and a cursed eye that can see the suffering souls within an Akuma, it's up to Allen and his fellow Exorcists to stop the Millennium Earl's ultimate plot: one that can lead to the destruction of the world. [Written by MAL Rewrite]

Extra bits meant to add to the Blue Seed story. Episodes 1-13 are extras shown on the video releases of Blue Seed in Japan. They take place after every other episode, such as Omake 1 follows episode 2. Episode 14 is an extra featured with OVA Blue Seed 1.5.