i'll see if i still have my archive; was a Relictors army using Dark Angels minis; went to a more "we can use deamonweapons as we're pure" look rather'n using chaosy bits
the Salamander, as the pointing arm just doesn't work with a shoulderpad, is likely to be stripped down and reposed, it's not as easy as just removing that arm (curse marine shoulderpads! curse them!)
so, throwing together some ideas for background;
X was an average Battle Brother in the Dark Angels, fighting for his Chapter for several decades.
As per any son of el Johnson, X went from Battle Brother to Sargeant, upto Veteran and, with being the sole survivor of the Ilandis V Massicare, holding the tattered Imperial Guard regiment firm until reinforcements arrived, promoted into the Deathwing.
It was after the Rites when X learned the Truth of the Fallen; how half the legion were swayed by Luthors' lies and that many of these traitors were still at large. With this knowledge that Xs' Faith was shaken.
Each of those brothers were trained and fought as he had. Each had spilt blood and fought in The Lions' name as he had.
Xs' combat efficiency dropped, the knowledge of the Fallen weighing down apon his mind, preventing him from working as an Battle Brother.
X spent time with the confessors and Chaplains, trying to regain his Faith, taking the sacred acts of flagellation to the point they were damaging, even for his altered physique. He would intone prayer for days on end untill his voice failed and the flagstones cracked under his weight.
Rumour persisted throughout the chapter of this Brother who had lost his faith, many putting it down to Ilandis.
The Dark Council, lead by Grand Master Azael, gave X leave to take the shattered remnants of his former Captains' Relic Blade and travel the Imperium, accompanied by a single serf, tasked with bringing Faith and Imperial Teachings to Mankind; such a humble journey and teaching others to reviere the God-Emperor, often by his very precense, may aid X to refuel his Faith, wherein he would be welcomed back to The Rock and have his Relic Blade reforged, a symbol of what he had regained.