So here's the jist of it. We're a Deathwatch Killteam, sent to Sector Curia, a fanon sector where all sorts of bad shit is going down.
Orks were always there, Chaos and Heretics are arriving, and an Inquisitor named Chance Poppycock requested a Killteam because he predicts that there's going to be a major Tyranid invasion of this sector.

This isn't going to be a super serious RP.
Nor are we going to bother with all the game rules and stuff, this is just purely for fun. 

Since this is a fanon sector, you get to make a fanon Chapter for your Marine. All I ask is that you make it in the form of this thing right [url=http://1d4chan.org/wiki/Space_Marine_Chapter_Creation_Tables]here[/url], so its easier for me to organize it. I'm going to be 'borrowing' your fanon Chapters for a homebrew Battlefront-2 esque strategy RPG, involving Sector Curia.