The boundary membrane of the energy realm interfered with the material universe.
The reason the Photonic Emperor hadn't entered the battle directly wasn't merely that the fighting was so one-sided he wasn't needed. He also had to guard against the great enemy of Chaos: Mortarion, the fallen Primarch aboard a Chaos Gloriana-class Titan at the heart of the Chaos Fleet.
That's right. The fallen Primarch Mortarion had arrived.
After the Chaos Gods were reborn, they spent several years slowly gathering strength. Their corrupted Primarchs also began to revive one by one. As the strongest Daemon Princes under the Chaos Gods, the Primarchs had all been deployed for this grand plan. Unfortunately, Mortarion had been unlucky: an Imperial reconnaissance mission had detected his movements, and he had run into the Spirit Machine Race fleet.
Having integrated Necron technology, the Spirit Machine Race fleet surpassed the Imperium's technology in some respects. The moment the Spirit Expulsion Death Zone appeared, even the fallen Primarch felt its effects.
"Legion Commander, we still can't reach our fleet. This area is already covered by the Spirit Expulsion field, and our psychic communications have been cut off," a Death Guard adjutant reported nervously. Gray-green smoke was rising from the rotting flesh on his body, dissipating into space.
The Spirit Expulsion Death Zone affected the entire starfield. Even the Gloriana-class Titan Resilience, corrupted by Nurgle's power, couldn't withstand the effects of this anti-Warp field.
"What about electronic communications?" Mortarion paced anxiously through the cabin. He stared at the projection of the World Engine displayed on the scanner, his heart shrouded in a pall of death.
"Legion Commander, there's no time. Our fleet is at least a hundred light-years away," the Death Guard Captain reported quietly.
The Imperium of Man in the Warhammer World hadn't developed Quantum Communication. The