The Emperor merely manifesting in a small girl stops time and destroys armies of Daemons

Colquan did not trust Guilliman’s motives. He was among the few dissenting voices among the Ten Thousand who queried what the returned primarch’s intentions to the Throne truly were. But he hated Chaos more. When Guilliman was snared and Mortarion landed in front of the primarch, he shouted out, urging his Custodians to Guilliman’s side. Their way was blocked by a wall of daemonic flesh. Four of the greater daemons still rampaged about the battlefield, shrugging off attacks that would shatter cliffs. Innumerable lesser fiends attacked from all sides. Two of his warriors were down, their golden shapes pressed into the mud. The thing he kept away from the Emperor’s last living loyal son growled and hiccupped its glee, and battered twice as hard at him with its long arms.

‘To the primarch!’ he shouted. ‘To the primarch!’

The daemon’s laugh clicked in a disease-ravaged throat. The damned thing seemed to have no voice of its own, expressing itself solely through violence and mirth. Colquan stabbed at it rapidly, driving it back. It shuffled around on its calloused lower limbs, evading every blow.

Then, at the height of desperation, she came: a young woman walking through the press of magic-born evils as if she negotiated a market crowd. A lone Battle Sister walked at her side, an escort who had become a herald. The girl was lit golden and walked lightly. Though the ground was churned to mud, her feet left no imprint where her companion slipped and struggled.

‘The saint of Tyros,’ he whispered to himself. He could not think of any other word.

Time slowed. The sound of the battle retreated to celestial distances. His spear ceased moving. The fight went from him. The girl took a hold of something inside him that made him forget where he was. Her eyes were hollows and her skin blotched. Atop her head her hair was coming out in hanks. The white shift she wore was marred by burns. She was falling apart, but around her was a soft lambency that grew as she neared the two primarchs, filtering between the combatants, setting the mist aglow, turning it from something foul to a net of glorious light. Colquan’s gaze could not leave her. The conversation of the primarch brothers faded from his hearing. The creature fighting him ceased to be a concern. He could have died then, killed by the daemon, but the Neverborn too was enchanted. The fleshless septum of its nose quivered as she walked past.It raised a quivering finger, and spoke in a hissing bellows voice, creaking and choked with grave dust.

An-ath-e-ma…’

One word. It swam across the air, wafting towards the girl as soft as silk carried off on the wind.

Time slid to a stop. Atoms stopped their motions. Light hung unmoving in the air. Sprays of blood made solid arches over the field, bolts hung midflight, the candles of their propulsive units stilled. An eternal cold gripped Colquan. Only he, for reasons he did not know, could look about him freely. All warriors were locked motionless in tableau vivant. Guilliman strained in bonds of living light. Mortarion had his scythe raised over his head.

But although all things had ceased their movement, so that the universe was trapped within a slice of a moment as insubstantial as a pict conjured from water, the girl still moved. She turned her head and looked at Colquan. In her face burned golden eyes as old as time, and from her mouth sprang the luminance of a star. Within his ornate helm, Colquan’s mouth fell open.

‘My lord?’ he whispered.

Dammed time broke through, crashing reality’s clockworks back into motion. Once more, the progression of events proceeded upon its unstoppable course.

Everything, having been stopped, rushed to make up lost seconds, and occurred at once.

The gangly daemon rocked upon its ruined lower quarters, amazed at what it saw. Colquan came to his senses before it did, and swung his spear around. The blade whooped through the air, connecting Colquan to the Neverborn’s neck by a bridge of arcing power. The daemon turned to strike back. As it did, its monstrous head fell from its shoulders. Its soul departed in a flurry of flies, and its body fizzed into nothing.

The girl stepped into the air above the melee. A dome of light sprang up from the ground. It expanded with light’s speed, catching everything in its shining radius. Men and Space Marines staggered. The Neverborn screamed. Mortarion’s weapon was caught the instant before it could descend.

A mighty wind blew up, blasting the fog away. Near the girl, the mist vanished. Further out, it flowed quickly back, revealing more and more of the battlefield, until only the farthest reaches were obscured. The sun broke through, and lit upon the broken plain. The lesser Neverborn evaporated like ice in a furnace, cast wailing back into the immaterium. The greater staggered, their bodies scourged by the girl’s glow. Their skin blistered. Their eyes cooked in their heads. They howled and screamed. Mortarion, being more daemon now than human, was flung backwards, his wings bent around his body. The bonds holding Guilliman shattered to glowing motes, and the primarch surged free.

Guilliman did not pause to consider the strangeness of his liberation, but strode forth immediately, brandishing his father’s sword.

‘Mortarion, enough! Now you will face me, and collect the wages of treachery,’ shouted Guilliman.

The Lord of Death staggered up to his feet and hefted his scythe, but he did not turn to attack his purer brother. He swung Silence backwards instead, its edge opening a slit in time and space. The daemon Ku’gath staggered through first. His palanquin was left in flaming ruins on the field, and his own back was afire.

I will face you, Roboute Guilliman,’ said Mortarion, ‘upon Iax. Follow me there, where we shall do battle the final time. We shall finish this, you and I. Your life will be forfeit, and I will take your kingdom for my own. On Iax!’

‘Stop, damn you, you coward! Come here and fight me!’ roared Guilliman.

Mortarion shook his head, and flung himself through the rift. It closed behind him.

‘Mortarion!’ shouted Guilliman. ‘Mortarion, you treacherous bastard! Come back!’

The primarch let out a wordless roar. Frustration and rage boiled up through his body. He tore off the helm of the Armour of Fate and cried out up at the brightening sky. His face was red. The cords of his neck stood out. Colquan had never thought to see Roboute Guilliman wear such an expression.

‘Mortarion!’