The Riot of Rotaria, Summoning Aversion Squadron

The Death Guard Praetorians gathered along with two of Nurgles Ascendant, preparing the world to be a well of energy within the system.
The ruined walls of the imperial sector crumbled, shattered by conflict centuries or perhaps even days ago. Some days the paint seemed... more vibrant.
A tingling sense of Deja vu swept over those in command. There was a presence here. Not seconds later the silence was shattered by the crack of a Suppression rifle. The glinting sight of the Primaris Marines rifle barely bucking. The crowd of plague marines all gazed inwards as the marine struck got up and stumbled to his feet. The icon of Nurgle on the marine behind visible through the rapidly healing wound. Muffled coughs of victory and cheers from the Nurglings nearby, as a Squad of Dark Angel Intercessors burst through the ruined wall of the bomb shattered building. The Nurglings proving to be harder to kill than the first Sons of Caliban had thought.
Continued firing from the Suppressor locking the Death Guard Marines with little to no cover. The Deathwing had arrived.
Charging forward into the grotesque Sons of Mortarion the 1st Company Ancients went toe to with best of the chaos monstrosities they used to call brothers. The first charge was brutal, the best of the Imperiums Armory brutally clobbered the almost silent hulks. Sick wet thunks as powered maces sunk into fleshy ceramite ripping the life out of those hit in the charge. As much as they took they in turn gave back, Mortarions Sons slogged back with their own terrible brand of melee prowess. Mutated limbs and whole new clusters of muscles allowed for inhuman speed for beings of their hulking mass. Not did one ancient of the Dark Angels fall, but was a brother returned to battle due to the quick work of the Apothecary.
A brawl of epic proportions, the two forces clashing under the dim cloud for the supremacy of first the planet, than the system.
Hours later when the dust had settled, craters still smoldering the Dark Angels stood victorious. Stopping the ritual before the fabric of space had rotted away to give way to Nurgles tide. Not without losses, the Sons of Caliban regrouped and sought to fortify the Rotarian hive as the Death Guard would no doubt be regrouping to take back the power source for the ritual.