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human
[Warhammer 40000 and Dead Space] What would happen if 97 Brother Moons showed up in the setting?

So Brother moons are basically like the tyranny hive minds and are horrible galaxy level threats in any other universe. They're able to travel at FTL speeds and ,in this case, immune to the corruption of chaos due to said hive minds and because they predate chaos.

This does not mean that they can't be hurt by chaos itself but merely that chaos can no influence them or corrupt them in any way.

The presence of a Brother moon results in any people in the system quickly go mad from the proximity. Surrounding systems are slowly being deceived and influenced by the moon whilst it's inhabitants are fighting the necromorphs. Furthermore the general location of a Brother moon can be traced as in this case Necromorph activity only starts to pick up within a hundred light years of one.
How do they effect the setting as a whole?
gpt
They'd basically be treated like agents of Chaos, and in all likelihood assumed to be either greater Daemons or the chaos gods would immediately set about working to incorporate them into their plans.  Even if Brethren moons did show up, virtually any single faction can easily destroy them; Orks would love the challenge posed by the moons, the IoM would probably just obliterate them, Tyranids wouldn't really care all that much and would probably either figure out a way to destroy the moons or to incorporate them into their structure since they seek biomass.  In the short period of time they exist, they'd probably be treated like weird manifestations of chaos or daemonic influence and would be quickly dealt with, unless they directly added to another faction's strengths, then they would be likely taken advantage of.  In no way is a Brethren moon's influence stronger than the influence of the Warp, so no one would really treat them like a serious threat.