Cowboy Bebop: Tengoku no Tobira

As the Cowboy Bebop crew travels the stars, they learn of the largest bounty yet, a huge 300 million Woolongs. Apparently, someone is wielding a hugely powerful chemical weapon, and of course the authorities are at a loss to stop it. The war to take down the most dangerous criminal yet forces the crew to face a true madman, with bare hope to succeed.
(Source: Anime News Network)