Come to the Canterlot Concerthall
Come alone, Tell No one
Hide your identity
Arrive at midnight
A cloaked figure reread the message on the card in it's hoof as the train it was riding, in pulled into Canterlot Station. Exiting the car, the figure saw that the station and street beyond was empty. A quick check of the station clock showed 11:30, nodding slightly the figure started towards its destination.
As the figure approached its destination, it noticed four other cloaked figures approaching as well. Each figure approached from a different direction. "More ponies answering the summons?" was the thought that ran through the mind of each. As the cloaked ponies arrived at the door, it was opened magically and without sound revealing a dark hallway beyond. As the last figure entered, the door closed and locked behind them. Seeing as how the only light was faintly showing ahead of them the five proceeded towards it.
When the five got close enough to determine that the golden glow that they had been following was the light from a horn, as brilliant flash threw back the darkness around them revealing the large room they were in and the figures of those within. Before them were three of the four ruling Princesses, Celestia flanked by Luna and Cadence in front of an ancient banner of the EUP Guard. As the five hurriedly bowed Celestia addressed the room while beckoning the five to stand, "For the past thousand years the Royal Guard has protected the throne of Equestria. When my sister was returned to me, a section of the guard was assigned to her. When the Crystal Kingdom returned, Cadence was appointed a guard from their number. Twilight Sparkle has thus far refused a guard, but as the dangers are many; we have decided to appoint her a guard without her knowledge."
During this announcement the five realized that not only were they surrounded by a mixed troop of Solar, Lunar, and Crystal Guard, but that a sixth cloaked figure stood of to the side. "As the foundation of the guard is an equality of Earth Ponies, Unicorns, and Pegasi; so we have selected you to be the foundation of the Twilight Guard. Do you accept? If yes, reveal yourself and state your acceptance," Cadance announced.
Slowly one of the cloaked figures withdrew their hood stating, "Ah'm her friend and if she asks me directly, I'll have to tell her the truth. Ah Applejack will guard Twilight Sparkle with my life." Shortly the other four figures in the middle of the room revealed themselves.
"Don't worry Applejack, the rest of us will cover for you. Rarity, and I will also defend Twilight Sparkle."
"What the hay AJ, you know we would never leave you hangin'. The awesome as always Rainbow Dash will defend Twilight."
"Um.....well....My name is Fluttershy and...and I will also protect Twilight."
"Mmhmm. Mhmm Hmm mmhm mhhm Mhmmhm."
"Uh what was that Pinkie Pie?" asked Rainbow. Pinkie responded with a muffled sigh and pointed to Celestia then to her own mouth which was apparently sealed.
Chuckling apologetically Celestia dropped the enchantment and uttered, "Oops, forgot about that."
Breathing in deeply, Pinkie Pie with as stern a look as she could give with one hoof over her eye repeated, " Well Duh. Pinkie Pie will of course protect Twilight, she the central character of the show. Pinkie Promise." To the slightly confused looks around her, she replied, "Whaaaaat?"
Rarity quietly asked her with a raised eyebrow, "Why exactly were you under a muffling enchantment in the first place, Pinkie Pie?"
Pinkie Pie just smiled at her, "Well actually it was Cadence's enchantment on my mouth, something about making sure I didn't say something I wasn't supposed to. Ugghh....Like please I can totally keep a secret! But Princess Celestia did put an enchantment on my hooves which made me have to walk all slow and ponderous like, writing something about my natural personality giving me away. If they wanted me to be sneaky, they could have just said so."
Rainbow quipped in jokingly , "Yeah but you probably would have done something involving a catsuit and nightvision goggles."
Pinkie Pie cheerily responded, "Oooo.....I totally have some nightvision goggles AND a catsuit! How did you know, Dashie?"
While Rainbow facehoofed, Rarity remarked to nodding Applejack, "Remind me to close the curtains to my boudoir at night."
Pinkie's face drooped at this, "Awww."
"And what about you?" Celestia addressed the last cloaked figure.
Removing its hood, the last figure said, "The Humble and Apologetic Trixie will protect Twilight Sparkle. And Trixie will move Trixie's wagon to the outskirts of Ponyville, where Trixie will perform for kids and not try to anger the townsponies. Trixie is good at the former, less so the later."
The five friends stared at her in amazement, broken by Rainbow Dash, "Trixie, why the hay would you want to protect Twilight? I thought you hated her?"
Trixie looked Rainbow in the eyes, "Twilight Sparkle saved Trixie from the Alicorn Amulet. Twilight has also forgiven Trixie for her misdeeds. For this Trixie will protect Twilight Sparkle." This revelation brought a mixture of surprise and acceptance from the others.
"You will need to take time out of your schedules to come to Canterlot to receive combat training. Just make sure Twilight is unaware of your real reason for coming. You will also be required to induct others to guard Twilight Sparkle in case you yourselves are indisposed. Perhaps each of you should pick another two ponies to start with? And try to make it balanced." Luna informed them.
This caused the new members of the Twilight Guard to start discussing likely candidates; with names like Lyra, Bon Bon, DJ-Pon3 (aka Vynal Scratch), Big Mac, Cloudkicker, and Blossomforth (aka the flexible one) to be bantered around. Before the inevitable disagreement over a certain gray mailmare; Rarity queried the princesses after remembering a certain mirror, "But what if Twilight needs, or chooses, to go back through the portal to her friends at Canterlot High? We would be hardpressed to insist on going with her, and she may suspect something."
Luna spoke simply, "No need to worry, Sunset Shimmer is already on the job."
Author's Note
Just my take as why there are no guardponies at Twilight's castle.
Also, I don't tend to see the IDW comics as canon; too many inconsistencies.