A part of a series called Axiom of Malediction on ao3.

To become a falling star upon a new world was something Gabriel hadn't expected to occur, but with nothing else to do in his now purposeless life, the "Righteous Hand of God," now a nameless soul will have to seek a new goal to keep himself driving forward. It doesn't help that he had found himself fallen into a country wrought with war and... Devils. It was not fun. I Do Not Own Arknights or ULTRAKILL, They Belong To Their Respective Owners.

Champions of a broken galaxy, mysteriously arrive at a planet as dark as their souls. Will they change the newfound world, or will the world change them? (Warhammer 40k x Arknights Crossover)

It's pretty much explained everything in the title so...

A science-fantasy crossover, that asks "what if the world of Arknights met the 21st Century United States." Beneath the classified depths of Area 51, a decades-long black project known as Project ARKSEK has achieved what was once thought impossible: the creation of a stable, functional gateway to another world. In the wake of this discovery, the United States mobilizes its most advanced and sophisticated military units and scientific minds to establish the first Human presence beyond the Gate. However, this new world known as "Terra" by its inhabitants is no empty frontier. It is a world shaped by its own complex histories, societies, nations, geopolitics, and scarred by Catastrophes. Home to diverse nations built upon the foundation of Originium, an enigmatic energy rich mineral that fuel its entire civilizations but also spreads a deadly disease that has no cure, known as Oripathy. What begins as an exploration mission slowly becomes something far more what the US could have ever bargained for in another world. Fraught with discoveries and dangers unlike anything humanity has ever encountered before. As American forces attempt to understand and navigate this alien yet familiar landscape, they will be forced to confront questions of morality, control, diplomacy and weighing the cost of intervention. What they will find on the other side may change the future of both worlds. For better or for worse. Every discovery always has a cost. And some doors, once opened, cannot be closed. For fans of speculative fiction. This work is fanmade fanfic passion project inspired by the world of Arknights, owned by Hypergryph and Yostar. All rights to the original story, characters, and intellectual property belong solely to their respective owners. I make no claim of ownership over any part of the Arknights universe. This project is created out of curiosity and admiration for the source material and is intended for fan speculation, appreciation, and entertainment purposes.