Story
Twilight, with the power of all the alicorns saw the blast Tirek sent, not at her, but to the Library.
As the library went up in smoke, leaving nary a crater, she stood there numb - replaying the last thing she’d seen before the library had been immolated.
In the window, where he’d gone to take refuge for safety had been Spike’s little, innocent, small terrified face.
She was numb. Then a heat in her gut roiled as she slowly turned to face the Monster Tirek had become.
The heat travelled from her stomach, filling her body as she trembled there, her eyes welling up in pure grief and rage as she snarled.
She raised her head even as her mane became fire, her eyes red with yellow for pupils.
Tirek had been gloating over what he’d done.
She shot forwards with a hard downsweep of her wings of flame, her horn blasted out with the power, but this time it wasn’t just with the power of the alicorns and something so weak as Friendship. No - this was something FAR more powerful.
She had raised Spike ever since the day she’d hatched him, and lately he’d even taken to calling her ‘Mum’ in his sleep.
This thing, this beast had taken her son from her.
The power this time she hit him with was charged with the grief of a raging mother!
“YOU BUCKING BASTARD!” She screamed as it slammed into his gut, she’d deliberately willed that power to return her friends' magics, even Discords - she’d deal with that traitor later.
She shot to the air, while with a mere thought she freed her friends from their confinements.
Spiralling back down she didn’t even bother to block his blast, her ‘fire-form’ deflecting the blast around her.
At point blank range she slammed herself at full strength and a blast of power into his lower back, a crater forming around him.
She ducked his grasp and another blast sent him high into the air.
Another glance to the library gave her the rage and grief for her next blast, even as she felt her friend's connection through the elements.
She asked the elements and they gave.
Opening her connection fully she pulled in all the magic she could, and sent the blast - this one didn’t knock him. This one didn’t break bones - no this blast was bigger than even Tirek and as it struck his screaming in agony form could be heard even as she poured more heat, rage, anguish, grief and despair into the beam vaporising the monster utterly, freeing everypony’s trapped magic.
Coming to land she turned, having lost her ‘flaming form’ but still holding pure rage and hatred in her eyes as she looked to Discord.
“Oh look at that! We won yay!” Discord said in his insincere tone waving a couple of pompoms before he was slammed into by a blast of power, knocking him to the ground as she formed her own bubble around him, stopping even his chaos magic working.
“Wait! please!” Discord cried, repeatedly clicking his claws.
She looked around, meeting the eyes of all the others who just nodded, even a yellow pegasus.
“Wait! Fluttershy, you promised! You’re my frieeeend! Friendship!” He tried widening his eyes to appear all innocent, getting a disgusted look back from the six who all had tears in their eyes.
“No!” Fluttersh shouted, moving to join the others.
“You freed them - because of your traitorous actions, Spike is - he’s NO! BUCK YOU DISCORD!” Fluttershy screamed.
Twilight again charged her magic, drawing on the elements, and this time the beam, though rainbow coloured, when it struck, didn’t turn Discord to stone - he slowly, though painlessly it seemed, evaporated - his molecules being broken down into their constituent protons and electrons dissipating to nothing.
Only once he was gone did Twilight turn back to the sight of the library before she collapsed, a scream of pure heartrending agony tearing from her throat as she collapsed, the scream of an agonised soul.
Even as she cried she cast the spell to return the other alicorns magic to them while the girls all moved to hold her.
Celestia and the others soon appeared.
“Well done my faith-oomph!” Celestia started to say in her usual gentle tone only to be collided into by a purple alicorn, sobbing her heart out.
“T - Twilight?!” Celestia asked, gently enfolding her in her wings even as Twilight's sobs stained her elegant form.
Looking up she saw the others who all had faces of grief.
“W - What happened?” She asked.
“S - spike was in the library.” Rainbow croaked out, causing Celestia to turn to look to where she expected the magnificent tree to be, only to see the crater stained by Tireks dark magic.
“No.” She whispered, turning to gently pull the grieving Twilight in even closer, holding her tightly even as cries kept tearing their way out of Twilight's throat, as if there was literally more grief in her body than it could handle.
Knowing there were no words that could help her student, friend and confidant, Celestia didn’t even try, she simply surrounded herself, the other alicorns and five mares in a large teleportation field and took them all back to her chambers in Canterlot Castle.
There she pulled Twilight close and just held her as the young alicorn sobbed her heart out, only opening her wings enough to let her friends in to help comfort her.
She held her own grief at bay, holding it in, trying to do her best to be there for the alicorn she had come to see as her own daughter.
She hoped eventually Twilight would learn to cope and carry on - there would now forever be this hole in her heart, one that over the millenia to come would only get bigger.
She hated that Twilight was learning this lesson so early, to treasure your friends and family as their time in your life could be so fleeting.
This was the main reason she’d sent Twilight to Ponyville, learn to make friends, so that when tragedy struck she’d also have ponies to lean on, to help her heal.
It was for this reason alone that outside of Luna and Cadance, Celestia always had her own group of friends to retreat too, and she knew that tonight she would desperately need them too.