Reborn in 40k Universe

After the protagonist sees a dream about the future, of all universes being destroyed by a grotesque being, he decides to go after it, preferring to be the hunter rather than the hunted, even if he ends up dying, ending up in the universe where the being has been corroding and gaining strength in the process for millennia. The protagonist ends up in a universe based on the 40k universe. Author; The universe will be based mostly in 40k I mean based and not in the 40k universe to have more freedom when writing and to be able to create a story more fluidly without having to worry so much about the Lore that let's say it is too big to take into account everything. Still, I'm waiting for your recommendations. the name is provisional as well as the cover.