Now, I gotta say, this idea you have got? Pretty damn cool. One thing worth note, for future reference, If a space marine has painted his armour to be black and joined the deathwatch, he would not be so forthcoming with what chapter he was from (ie. no running about yelling about SANGUINUS and stuff)
They like to keep that sort of thing a secret.

2781696
Maybe not the exclamation part, but having the symbol on your shoulder plate which all do, unless a Black Shield, is pretty forthcoming.

The Greyknight's existence is a secret outside of the Ordo Malleus even to other space marine chapters and the DeathWatch. They would not be announced by an ordo Xenos Inquisitor, and one that did know of them would be careful not to let such things slip, so they don't findthemselves on the Daemon hunters shit list.

Okay, I saw Deathwatch and was happy, as normal for them they keep one shoulder in the primary color of their chapter of origin, i.e. his right shoulder since he was Blood Angle would be Blood Red. Putting that aside, Blood Angle, I can already see him drinking blood as their vampire nature suggests in times of rage or immense hunger. I like the way you describe the battles, perhaps you should be more detailed in the appearance of other foes and draw the battles out longer when he faces foes of equal strength. That is all I got at the moment, good so far. (Blood Angles.... Not a big fan of them, more of a Raven Guard or Salamander guy, Grey Knights are cool too)