"Princess Celestia?" Twilight Sparkle called as she slowly pushed the throne room doors open, her friends close behind. Twilight spotted Celestia sitting alone on her throne, noticing a look of worry on her old mentor's face. Twilight quickly bowed at the foot of her seat, her expression matching Celestia's. The larger alicorn gazed down at her, unsmiling. "I am sorry to have summoned you on such short notice," she spoke gently to all of them, "but it seems a problem has arisen, and it may become very serious if we do not act quickly." The princess stepped from her throne and stood at their level, her head bowed slightly.
Twilight's eyes widened, but she held on to a respectful silence, waiting for her distressed ruler to continue. "Somepony has informed me of a situation," Celestia continued slowly. "Twilight, do you remember Princess Cadence and Shining Armor's wedding clearly? In the end, I foolishly never saw to it that Queen Chrysalis and her changeling army were gone for good. And now…they have returned."
Twilight Sparkle gasped along with her friends. Fluttershy tentatively stepped forward. "Queen Chrysalis is back? Then…how come we haven't seen any sign of her?" the pegasus asked softly, ears flattening with worry. Celestia closed her eyes, breathing deeply. "The Queen has not yet made an appearance, but a traveler spotted one of her minions walking through the Everfree Forest. The pony, of course, ran away before they could see if there were any more followers. We know for sure that it was a changeling, and it looked as though it were heading toward Canterlot. My guards cannot do anything but try and find this changeling and make sure there aren't any more of them."
Rainbow Dash narrowed her eyes. "Why can't we try and find the whole group and defeat 'em while they're weak?" she asked. Celestia shook her head, mane flowing silently. "We have no idea about the whereabouts of their current hiding place, although we know it is beyond Equestria. Have any of you seen anything suspicious lately? Anything at all?"
All of them shook their heads, except for Pinkie Pie. "Well, one of the cupcakes at Sugarcube Corner tasted a bit suspicious…now that I think about it…there was this green tinge to it…"
Everypony turned to stare at Pinkie. "What? Are you trying to tell me a weird-tasting cupcake isn't suspicious? If that isn't, I dunno what is." Rainbow Dash rubbed her forehead with a hoof and Rarity shook her head. "Oh, Pinkie," Twilight murmured, always so confused about her friend's constant cheerfulness, even in the darkest of times. Although, the alicorn did admit, most of the time it made her feel loads better when she was feeling serious or depressed. Laughter sometimes was the best medicine.
"What can we do?" Twilight asked, turning back to Celestia. "We no longer possess the Elements of Harmony, and our friendship is what helped us conquer Tirek before. We don't have another chest to open, and last time our friendship magic was triggered by unlocking the chest. How will we defend ourselves?"
Celestia blinked slowly, turning to gaze out at the Canterlot Gardens through a large stain-glass window. "That is why I have summoned you. I have a new mission for you, my little ponies, and it may be the hardest task I have expected of you." Applejack shook her head. "If you don't mind me sayin', Princess, we feel it's our duty to assist you, no matter the task. I'm sure it won't be too much of a difficult quest if we all stick together." Celestia smiled slightly, looking back at them. "Thank you. But before I give you your mission, I must tell you something. Something almost nopony knows. You see…there is a seventh Element of Harmony."
Everypony stared, complete silence ringing through the throne room. Everyone but Celestia had a look of complete and utter shock displayed on their faces. Spike clutched the sides of his head, horrified. Rarity had fainted, and was slumped at an odd angle over Applejack's back. Celestia held up a hoof as to keep them from starting questions. "There were not always only six Elements in Equestria…For you see, long ago…"
"Thousands of years ago, long before the rein of Nightmare Moon, there were seven Elements of Harmony. Uniqueness, Laughter, Honesty, Loyalty, Kindness, Generosity, and Magic. Using the Elements, Luna and I protected the land of Equestria from unhappiness and evil. But trouble arose when Discord began his war against us.
It was not long until he learned that we possessed the Elements, and that we were planning to overcome him. Thinking this would stop us, Discord somehow destroyed the Element of Uniqueness using his powerful magic. It was a struggle, but Luna and I managed to cast a spell to keep the Elements working. Although they no longer possessed their full strength, Discord did not either, for a lot of power was drained from him as he destroyed one of the most magical relics of all, and he was defeated by the remaining Elements.
Over time, the Uniqueness Element was forgotten, and the Elements have been six, instead of seven, ever since. The only ponies who still remember the Element of Uniqueness are Luna, Discord, and myself."

Twilight got settled into the idea. It all seemed to somehow piece together correctly and make sense.
"Is…that why Discord tried to keep us from using our Elements instead of destroying them?" Twilight asked, beginning to truly understand.
Celestia nodded. "I believe that Discord did not fully succeed in destroying the Element of Uniqueness. If you are still connected to your Elements, even though they are no longer with you, it would make sense that the other Element still lives."
Spike tapped his chin with a claw. "So that means there's a pony somewhere who's got the Element of Uniqueness in them…"
"That's right," replied the princess. "What I think is if you seek out and reunite the Element of Uniqueness, it will trigger your friendship magic once more, and you will be able to defeat Queen Chrysalis again, this time keeping her and her army away for good."
Twilight nodded to herself slowly. "This all seems to add up, but…how will we find this pony? Do we even have any place to start?" Celestia shook her head helplessly. "I do not know where you should look, but I believe this Element should still be in Equestria. It would make sense, as this is the Elements' homeland. This pony should be someone unique, and he or she should be able to fit in with you naturally well. I'm sure you'll know that it's them after a while."
Twilight nodded. "I'll keep in touch with you, and I'll be sure to send you a note if we have anything new to inform you about."
"As will I," agreed Celestia. "I have faith in you all. This task may take some time, and the key is to be patient. Let your feelings and instincts tell you what to do. Now go. There isn't any time to waste."