Nopony had yet discussed how to take care of the permanent Dusk that shrouded Equestria. It was clear Sunset Shimmer's magic was the cause, but her death didn't make it go away either.
Summer had an idea though, and she called the Twins over to discuss it. She soon left them there, and walked over to Princess Twilight, who was still with her Princess.
"Princess Twilight can you come help us a minute?" Summer asked with her head down.
"Of course" Princess Twilight said, and walked over to the others.
Summer explained her plan, and Princess Twilight gave it her enthusiastic support. It was worth a try anyway.
With the Rainbow Dash Twins in the center, the ten other ponies simply formed a circle while touching them, and instantly transformed into their Equestria Girls form, and simply all stood up and joined hands.
Both Rainbow's jumped up quickly and headed for the sky. Both of them left a rainbow colored trail behind them, which formed a magical conduit, keeping the circle complete. Everypony stayed in their Equestria Girls form.
Both Rainbow's quickly realized they could fly substantially faster as "people" as well, and they needed all the speed they could get.
The Rainbow Twins flew next to each other, and their path arched far to the right. When they were up near the bottom of the thick layer of the Dusk cloud, they quickly reversed direction and simply flew up into the cloud until they were in the center of it's thickness.
It must be noted that, inside the dense cloud, the Rainbow Twins could see nothing. This could only be done because they were true Twins and knew exactly what the other was doing.
The airborne Twins flew rapidly to the left, and then, at exactly the same time, split out of the clouds at a sharp angle. Equestria pony Rainbow flew down, and Equestria Girls Rainbow flew up, still out of sight.
Suddenly, the Twins flew back into the cloud at a 45 degree angle, and accelerated madly towards each other. The growing pressure wave in front of them indicated they were going very fast.
It is thought that a Sonic Rainboom is rooted in the vacuum caused by Rainbow Dash's sudden 90 degree turn. At the apex of this turn, the air around this vacuum rushes in to fill it, and then explodes out radially from that point. The resulting shock wave blasts out from that point, again radially, and with Rainbow colors. This radial wave-front travels rapidly away, and a loud boom is heard as well.
In this case, both Rainbows accelerated madly towards each other, into the cloud.
At the very center of the cloud layer, they met and both rapidly pulled away at the 90 degree angle. They said later that both of their feet actually touched, and they simply pushed off each other bringing even more acceleration, and so more vacuum, and etc.
This created a huge vacuum void that rapidly exploded radially outward, and also generated a huge, much larger 'boom'.
But the resulting radial shockwave wasn't Rainbow colors. It was the purest White, fading to Lavender then Purple. It was magic...
The magic in the shockwave set up a corresponding magical explosion across the entire depth of the Dusk cloud layer, immediately vaporizing it at the wave front.
The vaporizing of the Dusk cloud layer was accompanied by an almost deafening rapid popping sound as the magic reacted quickly with the cloud at the shock wave, dispersing the cloud.
The magical reaction simply accellerated the shockwave outward from the Sonic Rainboom and the reaction spread rapidly, radially outward from above the Commons of Canterlot.
Ponies that weren't zombies said they heard a deafening 'boom' followed by a deafening popping sound as the wave front raced past.
It was estimated that the shock wave covered the entire distance to the outermost edges of Equestria in around 1 minute.
As the wave-front blasted outward, the warm afternoon sun blazed down on Equestria in it's wake.
It was a
Blind,
Double Reverse,
Magical,
Sonic Rainboom.
This feat would probably never be duplicated in Equestria's history. Ever.
Awesomeness times two!
In the Equestria Girls world, if you were watching something, and it was awesome, you clapped.
The four Equestria Girls were elated, and rapidly dropped hands and applauded madly.
The Circle was broken.
The Rainbow Twins turned back into Ponies.
Equestria pony Rainbow Dash simply kept going without missing a beat.
Equestria Girls Rainbow became immediately disoriented, and was soon spinning wildly, falling fast, screaming.
Summer herself was quickly in the air, and headed for a spot to intercept her fall.
Summer turned quickly into her Equestria Girls form, and flew even faster. Both her Cutie Mark and head were warming. She wasn't sure why, but would yank Rainbow's Twin from her death if she could.
She did not need to worry.
Equestria pony Rainbow immediately sensed her Twin's trouble and quickly dove rapidly into a slow arc that would allow her to intercept her falling Twin, and gently at that.
Raimbow eased under her twin, stopped her spin, and as she slowly glided up away from the ground, she gently launched her Twin up off her back and said "Flap your wings girl!"
They were both quickly off, flying together again.
Summer turned slowly away, back towards the Commons and just flew. Summer loved flying.
Summer did a tripple barrel roll, and in the middle of the second one, she changed back into Equestria pony from, and then completed the rolls.
Both Rainbows were right behind her, side by side, shadowing her every move.
Summer didn't mind, she was just flying calmly because she loved to fly. They just followed her for a while. It was fun.
Flying over the Commons, she even saw both Fluttershy Twins up off the ground a little.
The other Twins were sitting together enjoying the show.
Summer landed, and sat with the other Twins and just watched.
Spike finally woke up, and ran up at this point, and hugged Princess Twilight, and was soon on her back where he belonged.
As real dusk began to settle over Equestria, Princess Celestia called Summer Rain and the Twins over. Princess Twilight and Princess Celestia had been talking.
"Summer, how long have you and the Equestria Girls been in Equestria, do you think?" Princess Twilight asked.
Summer looked around at the Equestria Girls for a moment and said "Two days I think."
Princess Celestia gasped in disbelief...
"What committments will you face when you return?" Princess Twilight asked again.
"School..." Summer and the five Equestria Girls said at about the same time.
"Ugh, new class schedule for me too..." Summer added.
"Ok, well this is what we are thinking. We agree that Equestria really needs to celebrate this amazing victory, but Equestria really needs cleaning up right now" Princess Twilight said.
"I also realize the Twins would really appreciate more time together before you six head to the Portal and return.
"Let's do this. Let's plan on meeting at the Portal tomorrow at about this time. We will then send you back to the Equestria Girls world. After the next week of school, we want you to return, and we should be able to celebrate then. From now until tomorrow evening, the Twins can spend time together. How does this sound?"
Equestria Girls Rainbow Dash spoke up and said "I think we have a break after this next week of school anyway, so we should be able to stay for a while. That sounds good."
The Twins were all very excited at this.
Shining Armor and Princess Cadance stayed in Canterlot for the moment, managing the task of rescuing Equestria and it's foals from the Green eyed zombie pony parents.
"Ok, let's head to the Train Station, and see if we can get a ride to Ponyville." Prncess Twilight said.
The same Train and stallions were there and ready, happy to return the pony warriors to Ponyville.
The Train was soon on it's way, and the Twins quickly fell asleep together as before.
Spike was quickly asleep too.
Princess Twilight and Summer were sitting together up front.
After silence for a while, Summer said softly "Thank you Princess... for everything..."
Princess Twilight hugged Summer, and they both just cried softly together for a while.
Princess and Summer were soon fast asleep next to each other like the Twins.