http://www.blacklagoon.jp/
Plot: Okajima Rokuro is a businessman in a city of businessmen. One day, in a business deal gone bad, he gets captured by a group of mercenaries who operate under the name Black Lagoon. Stuff happens. He gets taken in by the group and begins working with them, and is dubbed "Rock". The rest of the series concerns itself with warring gangs and the goings-on of the criminal underworld.
That's Revy in the picture above. She's f'ing crazy. She's wonderful.
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I just finished this series last night. It was slow to start - the first few episodes left me cold, but the second season (episodes 13-24) was amazing. It's action-packed, soaked in violence, and there's enough profanity to make a sailor blush. It's great. It's mindless entertainment. The arcs are short so it's really easy to watch. The thing I loved most was the development of the friendship between Rock and Revy - it's surprisingly subtle in an otherwise garish series.
Odds are they'll make a third season. I can't wait.
Why are you not watching this right now?