The Iron Host pt1

Over the few years of playing my Chaos Marine army, i have developed a quite in-depth background for them.
...do you guys wanna hear about it?
Of course you do.
The Iron Host was originally a splinter cell of Iron Warriors, their ship had been sent to set up a base on a frozen wasteland of a planet to keep eyes on the other inhabited world in the system of Hastia. 21 marines made planetfall with dozens of cultists and a couple priests of the Dark Mechanicus to observe proper building technique. No sooner than they had put the finishing touches on the stronghold and were just setting up a defense perimeter, than the shiney new base power generators were targeted and blown to all hell by an orbital laser. The vox erupted in "what the hell?!" and was silence in the other end. Soon, another barrage came, this time a virus that had recently produced to be used on the other inhabited planet in Hastia. Most of the mortal cultists were liquefied upon contact with the stuff, a few others watched in horror as they withered away, being eaten away by a green spore.
The marines, seeing this, NOPE'd back to the dead fortress and held on for as long as they could. Weeks went by, each of the remaining 20 (one was sealed outside as another barrage started raining down) slowly started decaying;
Their armor was sealed to outside air, but gradually the spores in the air clogged up all the recycling apparatuses and ventilation systems s much that the seal needed to be released.
As spores made their way into the bodies of the marines, the first symptom for each was extreme cold followed by a plethora of symptoms unique to each marine. One couldn't feel his legs, another his arms. One become paranoid of being the first one eaten and convinced himself he would take the others out before allowing himself to be eaten. So he went to the armory to load up and was betrayed by gravity as some large and very heavy storage units fell onto him.
Eventually they all died. The last one to do so was Anthrallis, who had survived a full standard terran week longer than the rest. As his dying breath escaped him, he saw something form from the spores in the air. Definitely something humanoid in shape but his vision blurred and he slumped to the ground.
Threek weeks later, according to the chronometer in his helm, Anthrallis awoke and saw the humanoid shape again in front of him. And he felt... Better. He talked and argued with the daemon for some time in the silent fortress, and eventually came to terms with it all:
The virus that was launched in the planet was created using some warp technologies he didn't understand that involved tiny cell-sized daemons of nurgle and ork replication genes. Normally the virus would make contact from skin or breathing, eat a cell reproduce, and continue on until the entire organism was replaced by the spores. The daemon Anthrallis was speaking to, revealed itself to be the progenitor of the cells used to make the virus and claimed that as each marine was devoured, their DNA was kept somehow inside the spore. Since all the marines were in complete armor upon death, the spores had no room to spread out and maintained shape. (Not being in a ridged suit of armor to keep the shape of their bodies was how the cultists became puddles) the residual dna in the spores ended up, by some machination, knowing what the purpose of the marine cell they replaced was, and acting like them. Thus, a skin cell eaten by a spore cell had it's job replaced by that spore.
In short: they had become "fungus men"
As time went on, the other 19 woke up and they all took evaluation of the situation. They were alone, abandoned, and betrayed. So they continued adding to the fortress. Two of the marines, no longer terrified of death to go outside the walls, repaired the generators and got things going again.
Oh, and they changed their name to the Iron Host because A) they're still iron warriors and B) because they are each host to an amazing gift from Nurgle and only want to share it.

That's it for now, ill add more later...
Have a good night, Interwebs.