One Hate (Heroes of the Space Marines)

On the planet Syral the Imperial Guard are fighting a losing battle against the ork hordes. A squad of Crimson Fists arrive at what seems like a critical moment, and they look to be Syral's last chance for salvation. However, the Crimson Fists have other motives, and they will not be deterred from their greater goal.

Read it because
It's a tale that showcases the bitterness and resentment the surviving Crimson Fists feel towards the greenskins, and the effect that has on both them and those they fight alongside.