This is the animated version of an Omake(Special Chapter) that came out in one of the volume release for Black Lagoon. There's one Omake per volume and they were all animated for the Blu-ray release of the Anime.
I can't believe the same Toyoguchi Megumi actually voiced Revy, who also voiced Kirino from Bamboo Blade. And to think I could hear Kirino's voice in it too, LOL.