This is pure heresy! Where can I get some more?

I'll be honest, I don't really know much about "Warhammer".
I only became somewhat interested after seeing some of the images of the Space Marines online, so I took some time to read up on it. All I can say is that the sheer scope is mesmerizing, although the 40k universe as a whole is an utterly terrifying one to contemplate. I can't really say how faithful this is as a Warhammer story since I don't know all the nuances of that series, but as a Superman fan, though, I think this does the character justice. I mean, I get that 40k is supposed to be grimdark, but by the same token, there's plenty of darkness in the real world. Sometimes people need hope, and that's something Superman represents. Personally I would LOVE to read a Superman story where he is alone in the 40k universe. Not so that he could just punch orks and shit, but to have him interact and explore these worlds, maybe the story showcasing how his presence affects them, both positively and negatively, but I'm digressing.

All in all, it's a good story.
Out of curiosity, have you considered doing a follow-up?

No, just.. no. I loved the Mass Effect one. That worked. It worked well.
But 40k? No.

Yes, the Imperium is harsh and fascistic, but it's also necessary. By teaching its citizens to hate the xeno, they ensure that when it comes time to fight xenos who cannot be reasoned with (orks, tyranids, necrons, chaos, dark eldar...) then the troops will hate them and thus not run screaming like any sensible person would. Remember, living in peace with the xenos, requires them to want it too. You try persuading the eldar that the mon-keigh are worthy of being allowed to share the same galaxy as them. At best we're pawns to be moved in order to fight their wars for them. At worst, we're competitors.
By teaching people to worship the Emperor, they strengthen him. He's doing his best! He's dying on a throne, holding back Chaos. Taking away faith in this universe weakens the subject of that faith. By doing this, he's directly increasing the liklihood of chaos incursions. By having allof those people living free, without their dogma, he's allowing chaos direct access to their minds. You don't have to worship chaos to let them in - it just helps. Those worlds would be overrun by now.
I imagine that these worlds aren't sending their share of weaker psykers to be consumed by the Astronomicon? Without that beacon, travel in the 40kverse becomes impossible.
The 40k setting is one that is harsh and unrelenting. It requires the individual to be sacrificed in order that the many survive. It's survival of the species, not the person. Having a do-gooder running around, trying to 'fix' this is just going to make things worse, unless the true reasons for the galaxy being this way are dealt with, and that would require genociding a number of races, and also lobotomising or heavily drugging every single one of the remaining ones so that they were calm and emotionless, and so weakened the Ruinous Powers to the point where they faded. Which would be a job that took centuries at best.
The best alternative would be to carry people to another galaxy, one where Chaos does not reign. It would have its own problems, and the Tyranids would be just as dangerous, but that's the only other solution.
Nice though the idea of Superman being a beacon of hope is, in this setting, where he goes, Chaos will follow. Everything he does will lead to destruction. His naivety will be his undoing.
And yes, he's physically resistant, but against any strong psyker, sorceror or demon, he's going to be so much roadkill.
On the plus side though, I loved the Mass Effect insert story.

Proof that Superman's good heart can brighten even the darkest timelines.

Argh, I want more of this universe, too! From Superman's viewpoint, possibly; how he got there, how he feels about the whole, well, EVERYTHING of the WH40K universe, how he starts, his deeds, the reactions of all the other races from first hearing "tall tales", to seeing he's real, to what they try to do in response; how the Emperor himself would react, as we all know that it wouldn't be right to not have him be finally healed and such for such a major change; the Chaos gods; hell, if he does enough, Superman could start gaining more power from all the belief in him

Just...so much that could be explored in this kind of crossover...overloading my brain...

Sweet history man

That is a dark as fuck ending. Sure Superman achieves more and asks for less, but your pov character clearly traded one obsessive religious reverence for another, and he thinks it freed him.

I wonder if he'd like up to join the free systems infantry if Superman needed help covering more space as their territory expands...

~ja ne

True that. Superman by this point is likely at his I ate a sun stage of power and thus unlimited. Time and space are but daliances to him. Rather cool idea though.

...Honestly, I'm wondering what'd happen if Superman wound up facing the Emperor himself or something... And how Supes got there. But yeah.
GREAT read.

What a fascinating story. I love Superman and it was a delight to see how his presence would interact with the world of WH40k.

his cute little mind was blown

This is how superman should be. Not some all-powerful god that can never falter or bend others to his will, but a being that just wants to do the right thing because it's the right thing to do.

Thats what superman is: a symbol of hope.

And in a universe as dark as warhammer 40k, hope is practically a forgotten dream.

I love this story.

Fuck yeah. Golden age supes.

Beautiful. Simply beautiful.