Things might have turned out better for both realms, but this is a crossover with RWBY and 40K; there are going to be some heart-wrenching moments.
In Perturabo in Remnant
- The snippet "Of Ponies and Princesses" is pretty sad. The village of Kuroyuri, Ren and Nora's home, was visited by Perturabo who had hoped to supply the people living there with high-tech weapon systems to give them better protection from Grimm. His offer was refused because the people in charge didn't trust that he wouldn't try to exploit them with his merchandise. Just like in canon, Kuroyuri, gets attacked by a horde of Grimm and is destroyed. While Perturabo and Penny are able to drive off the Grimm, they're only able to save Ren and Nora, and Perturabo blames himself for failing to convince the villagers to accept his systems and thereby allowing what might have been a preventable disaster from happening.
In A Crusade of Blood and Dust
- The deaths of Ren and Nora during the Siege of Terra is absolutely tragic. The snippet is told through First Captain Sigismund's point of view and it starts off as bleak as it can be. Traitor Iron Hands Astartes are attacking again and the two Hunters are locked in pitched combat. Before long, a Chaos Champion engages Ren and Nora; they're both incredibly skilled fighters, but the Champion gradually gains ground against them. Sigismund sees them struggling and begins fighting his way through traitor forces with increasing desperation, praying that he arrives in time to help them. In spite of his best efforts, he is too late and both are killed by the Champion.
- Rogal Dorn managing to strip Angron from his daemonhood and utterly destroy him was supposed to be awesome, and it is... But as Angron loses his unholy powers and rage, he regains his sanity and apologizes to Dorn for having been so awful. Poor Dorn is left completely broken from this brief glimpse of the man his younger brother should have been, and since the Fulgurite destroyed Angron's soul, he doesn't even have the comfort to know him at peace — because there's nothing left from Angron.
- The Spaces Wolves attacking Prospero, from Leman Russ's viewpoint. In this timeline, Magnus actually didn't do anything, bowing down to the verdict of Nikeia. Yet his homeworld is attacked by his brother's legion because Horus wanted him out of the way and played on Russ' Fatal Flaw of blind obedience to make him assault his own brother. Described by one reader as the greatest My God, What Have I Done? ever written.
- Konrad Curze having a nervous breakdown while on a mission with Sanguinius, confessing he constantly has visions of his impending fall into darkness and begging for a Mercy Kill. The Angel basically learned one of his most "difficult" siblings had genuine mental problems yet he didn't see that until said brother finally went suicidal.