"Terrible!" Luna yelled to her sister over the roar of battle, then paused to kick a zebra in the face. "When we asked for thy backup plan, thou shouldst have said this was what it was! Terrible!"
It was true, unfortunately. Luna knew she should have tried harder to override Celestia's orders - the older sister had always been the lesser at everything from chess to true warfare. That was proving to be the case once more - the Guards had been driven off the hilltop after a botched counter-attack, and were pinned between zebra forces and a firestorm likely fed by the alchemy supplies at Ponyville Elementary. The Princesses had stayed with them to protect them from wholesale slaughter, but they were still down to ten, after several messengers attempting to fly to Canterlot or Cloudsdale for assistance were shot down. One had finally gotten away, but Celestia flew into a volley of arrows to ensure it - and not all of them were deflected by her armor.
A quick glance revealed Twilight's rampage could no longer be counted on as a wild card, either - the zebras could not approach her, but had lured her into the Everfree, where she seemed to be starting a forest fire. And as if numbers and injuries weren't enough, Luna noticed magic wasn't working against the higher-ranking zebras - it felt almost as though they did not exist as magical entities at all.
"I know, sister. I apologize." Celestia wheezed with every other word. Her injuries were starting to take a toll, though her raw power permitted her to continue fighting as she called back. "But I will not allow my ponies to die!"
"Then it is time for thy silver tongue to save them." While she had always been the better at war, the younger Princess knew she was far outclassed in duels of words and diplomacy. Luna channeled power into her Royal Canterlot Voice. "Parlay!" she roared over the battle. "Disengage immediately!"
The zebras seemed interested, as fighting died off in seconds. Guard and Stripe alike watched each other warily as they parted lines and the last arrows fell. One zebra, decorated in black-feathered armor but otherwise unremarkable, approached the Princesses' position alone.
"Send forth your leaders, and let us trade words, for I am the one in charge of these herds."
"Zecora." Celestia advanced a few steps. Though her body was hurt and tired, her voice retained its warmth and regal calm. "I am very disappointed."
"If you are hurt, or even surprised," Zecora said with a shrug, "you should not have ruined the homeland I prized. Will you surrender, and make your deaths swift? I shall not listen to lie or to gift."
"I believe that when you hear what I have to say - " Celestia was cut short by the fiery green pop of another scroll appearing in front of her face. There was some unrest in the zebra lines, but with a wave of her hoof, Zecora settled them. Celestia gave her a gracious nod before she unrolled the scroll and read silently.
Dear Princess Celestia,
Derpy couldn't get to you. Died on top of me. Her message is next.
Your faithful subject,
-Spike
Another scroll, spattered in places with fresh blood, appeared almost immediately after:
Princess,
Scouts lost. 9/10 dead. Zebras at Manehattan and Fillydelphia. More moving on Vanhoofer.
Zebra balloon units moving on Las Pegasus and Cloudsdale. Wonderbolts, Night Guard lost in action.
Cloudsdale evaccing. Las Pegasus already empty.
Couldn't do better. Sorry.
Faithful in death,
-Polaris
Luna, reading over her sister's shoulder, frowned. Things must be dire indeed if Equestria's clumsiest flier was the one entrusted to bear such vital - if disappointing - information. There was little that could be done about the zebra military now. They must have crossed the borders, which her sister always insisted on not guarding as a gesture of good faith, at least a week ago.
"We wish to discuss terms," Celestia said. Her voice had turned soft, a sign of the impact of the ill news.
"In speaking of terms, we shall have none," Zecora retorted. "You shall have lost, and we shall have won. We have the strength to do as we wish. All I may offer's a sword and a swish."
"And I have the strength to do more than what's passed. If you'll accept nothing for the lives of my ponies, I can do far worse than run and hide."
"For our revenge are we all willing to die. If you will not surrender, it is time for goodbye." Celestia raised an eyebrow.
"Do you speak for every stallion, mare, and foal? What of your mothers and elders?" Celestia was bluffing. She had to be bluffing. Not even the sister who cast her into the moon would truly threaten children, Luna knew. "Your numbers depend on the food we provide. If you kill my subjects and ruin this land, you will face famine unlike anything seen in a thousand years." The zebra frowned.
"The lessons of Hellfire are hard to forget, but we can take what we want to have our needs met."
"Surely you remember to whom you speak. I am your so-called Queen Hellfire, demon of the sun. I care not for threats, but you know what I can do merely by accident. I am the one responsible for your suffering and hatred. I am the one who burned your lands and your people." Zecora twitched angrily, but Luna cried out in alarm at the direction she sensed Celestia was taking.
"Sister!" Celestia seemed to pay no heed to her.
"I am the only one who has ever been at fault, and I will give you a choice. Allow me to surrender my person in exchange for my ponies." Celestia drew herself up to full height, her pearlescent mane and tail briefly igniting into dozens of colors of flame. "Or discover what the one who destroyed your nation by accident can do, when offered nothing to lose!"
Luna and Zecora both took steps back in shock. Did Celestia really just say that?
"You're - " Luna started, but was cut off.
"Sshh." The younger princess opened her mouth to protest, but saw her sister wink, and shut it again. I hope you know what you're doing.