Heir to the Crystal Empire

An alert was sent out right away, preparing the Crystal Empire for the upcoming attack. Shining Armor raised his magical barricade without delay, and shortly after began positioning what few ponies he had under his command: A motely collection of barely trained crystal guards, rarely active Equestrian guards, and a small smattering of volunteering civilians. Cadance helped the rest of the population find shelter, before flying to the Crystal Heart, which they all knew would be their final defense if the barricade fell.

The Empire's plan was basic, but with little in the way of defensive resources aside from their prince's shield, it was all they had: Lieutenant Flash Sentry was to fly to Equestria as fast as possible and alert Celestia, while Shining hold the barrier for as long as possible. Fortunately, they'd made preparations after the battle with Sombra for this situation: Cadance had cast several spells on Flash Sentry that would allow him to fly without need for sleep, food or water. In addition, the Royal Couple had a strategy in place to switch off shield duty. However, in light of the fact that this mysterious General Thaw was a non-magical earth pony, Shining Armor had made the call to raise his shield first, as his was better at repelling physical threats, while Cadance's wall of love better reflected dark magic and evil.

On a snowy hill beyond the magic shield, a unicorn stares down at the shield with contempt. Oh, what she would give to display her raw power, to sunder the magic shield with her raw power! But, the fool Thaw had devised a workable plan, so she would humor him, for now.

"Are you ready, Sunset Shimmer?" Asked the other pony behind this attack. The unicorn threw back the hood of her arctic cloak, exposing her bright red hair to the chilly air. Her only response was to crack a sinister grin. "Begin the first volley."

Behind Sunset Shimmer, five more unicorn mares, covered head to hoof in tight fitting black tunics, stepped forward in unison. A green glow filled Sunset's eyes, and shortly after, the same glow filled the eyes and horns of the unicorn troops. In perfect sync, blazing red magic rockets shot out from their horns, and arced towards the stalwart wall.

Shining Armor caught sight of the projectiles approaching, and added a burst of reinforcement to brace for impact. The magic missiles impacted the shield, and detonated in a blazing burst of red light against the magic shield. When the light had faded enough for Shining to gaze upon the impact site, he cracked a confident grin upon confirming that the magic spells hadn't made a dent.

Thaw remained unconcerned by the strength of the barricade. He gestured to Sunset Shimmer. "Begin the second salvo." In response, Sunset's horn glowed brighter, and the five other unicorns fired off another round of magic missiles.

Though he was feeling confident after stopping the first barrage, Shining Armor refused to get cocky, and braced his shield for the second burst. The rockets detonated in another blinding flare, but this time, when the defenders could return their eyes to the impact sight, their eyes widened in horror. The magic missiles had gone through the barricade, and where now descending upon the city below.

The five missiles converged on a singular crystal tower, erupting in magic fire on impact, shattering the structure completely, and scattering the shards into the street. The Crystal Guards manning the barricades recoiled in horror, their moral plummeting, and even the more disciplined Equestrian soldiers could not quite hide their worry.

Shining Armor's mind went into overdrive, trying to determine how this was possible, and what he could do in response. His thoughts were interrupted by an approaching crystal pony. The pony came to a halt, and held up the communication crystal. The royal couple had each cautiously examined the crystal to make sure it had no dangerous spells attached, and it seemed harmless, but had confined it just to be safe. It was now glowing. The crystal pony set it down and scurried away.

Before Shining could speak a word, the projection of Thaw returned. "As I have demonstrated, Captain Armor, your shield offers no protection against the Crystal Army. Lower the barrier and allow my forces to occupy the city, or I will resume the bombardment."

Shining Armor's first thought was keep Thaw talking. Cadance's shield might stand a better chance of repelling whatever magic Thaw was employing to break his barrier, and he hoped his wife had the same thought and was drawing up power from the heart to project the shield.

And should the worst come, every second he stalls them is one less second the ponies would have to spend in slavery, waiting for Equestria's response.

"What happens then Thaw? How do you plan to occupy this entire city? Sombra didn't have an army, and there's no way to keep a large enough force alive in the tundra."

"You are attempting to stall me." Thaw stated bluntly. "The messenger you dispatched to Equestria has already been captured, and your wife will not be raising her barrier. Lower the shield or I will resume my attack."

Shining's eyes narrowed. "What did you do to my wife?" He asked, cold anger mixed with fear in his voice.

"She is unharmed. Physically, at least. The sooner you lower the shield, the sooner you will find out." Shining Armor was torn, anguish and helplessness overwhelming him. His wife was in danger, his shield was useless, and his messenger caught.

Despair filled the captain's voice. "Alright Thaw, you win."

And with that, the shield fell.

Throughout the city, the Crystal Ponies looked on in shock and horror as their sole defense fell. Some screamed and panicked, while most fell to the dirt, hoping a display of servility would earn some manner of mercy. The few guards rushed to the palace, to find what had befallen their captain.

Before dissipating, Thaw's projection spoke one last time. "We will meet at the base of the palace to discuss the terms of surrender."

Thaw entered the city with a modest procession. Sunset Shimmer strode besides him. Behind them, were ten of the back clothed unicorns, in two ranks of five. Rounding out the parade, to the shock and horror of the kneeling crystal ponies, was a small group of their kin, clad in black and blue armor.

The group stopped at the steps of the palace, where Shining Armor and the Equestrian guardsmen waited.  "Your wife should be joining us any minute, captain." Thaw stated, and before he could reply, the entrance of the seat of the Empire's power opened wide, and out trotted the terrified princess of the nation.

She was surrounded by chittering, black carapaced changelings.