They came from behind

It was a dark day. The ground was unstable, and the winds of change where blowing. The Shas'O didn't enjoy the taste on the air. It was like a portent of doom he just couldn't shake.

And the blood rains down

In the far distant future, there is only war. Where untold trillions toil for the machine of war that is the Imperium of Man, where daemons bleed from the warp to slaughter in the thousands, a soul is nothing, but fuel for the fires of war. Amid this eternal carnage a strife lies Gore Swirl, a world that is not a world, a constantly changing plain of destruction, a guardian to a portal deep into the warp. He who controls the plain, controls the portal, and the destiny of the entire sector.
When battle was first joined, the Tyranids and the Sisters of Battle both fled the field, leaving only the Tau and the Acolytes of Change of the Chaos Space Marines. As the two remaining titans faced off once again to claim Gore Swirl, another army made planet fall. The Blood Angels chapter had come to play.