I don't know if there's a story to go with this but I'm starting to formulate one in my head.
Cas is a very respected ship captain with the galactic government, he's one successful mission away from being promoted to admiral of the whole fleet. The mission they give him is this: There's a bounty hunter going around, working on the fringes and taking out a lot of people that the government needs alive (informants, officials, etc.). Cas is charged with taking out this bounty hunter. An easy mission, he's go this promotion in the bag.
He tracks the bounty hunter, an awesome game of cat and mouse s he chases him through the stars (thats about where the picture is i think, dean's got this shadow.) Eventually Cas finds the bounty hunter, who, after an epic fight scene, gets captured. What Cas doesn't realize is that he's this hunter's next target.
So then Dean's in cas's prison, except hes not. He got out and is now sneaking to Cas's room to go and take him out. They talk, dean tells cas some sob story about why he doesnt trust the government, cas tells dean how hes misguided, that the people hes working for are /way/ worse. they end up teaming up to break down the crime circle and the oppressive government, freeing the galaxy from the their influence.
They end up together, the end.
I'm sorry if I broke any unwritten laws by posting this or somehting, i totally do not mean to distract from this awesome piece of art (seriosuly only the /really/ good stuff inspires me to write things like this so go you *high five* )