It had been many, many moons since that fateful day in Ponyville, when Princess Twilight and her closest friends fought against a great evil. And all was peaceful in the Land of Equestria. All the princesses were relaxing, after all the encounters with the mighty foes, they felt everypony should have a day of relaxation. Luna especially. This was the day after 7 year anniversary of the day she had been freed from her Nightmarish form. Thanks to her friends and sister, she was able to overcome her guilt of being who she was.
The last remnants of the Nightamare Force had been sealed away in the castle. And Luna, she couldn't be happier. Within these 7 years, a colt had won her heart and became her special somepony 6 years ago. His name was Shadow Comet, a pegaus, who surprisingly looked a lot like her, and equiled her in hight, with a comet for a cutie mark. 1 year later, Luna had been blessed with two adorable little foals, who inherited their mother's alicorn gene. After having seen that their cousin Flurry Heart had been born alicorn a year before them, this had come as less of a shock to Luna, but it made her all the more happy, for even though she knew she would loose her mate, she would not out live her Angels of the Night.
She named her son Moon Dust, for he always tried to get his hooves on the moon dust Luna had brought back from the moon for a keepsake. Her daughter's name was Eclipse, for she and Moon Dust had been born during a Lunar Eclipse.
Getting back to the present, Luna knew her two little trouble makers were galloping around the castle, and could picture what Blueblood would look like every time they pranked their mortal cousin. No matter how hard he tried, he could never get the royal sisters to scold them for their antics. They were too funny.
Today though. Blueblood was not on their minds. They were exploring the castle. It was the one thing on their to do list they had not accomplished yet. They were seeing many things they had seen with their parents when they weren't busy, but there were some other areas that had yet to be explored. With Luna taking it easy, and Shadow Comet helping Shining Armor dealing with some disputes among the Royal Guard, there really weren't many ponies who could stop them. As always, they had slipped away from their caretaker who had drunk a glass of water that had some star dust sleeping powder in it and made her fall asleep. This would not surprise Luna too much when she found out of course. She knew it was bound to happen sooner or later.
Moon Dust and Eclipse came upon a door that, well, seemed like it hadn't been opened in quite a long while. Curiosity got the better of Moon Dust and he opened the door. When they opened it, what they saw amazed them. "Wooow," The siblings gasped in unison.
Everything here appeared to be from times long ago, back when Equestria was more on alert in a time of great conflict. Some relics even seemed to predate Celestia and Luna themselves. As they wondered through, they saw what appeared to be a large chest with alicorn writing all over it. But something made them feel uneasy. They didn't want to get near it, as if some dark presence surrounded it.
They decided it best to leave it untouched. They found many other interesting relics that were amazing. One appeared to be armor that seemed to be about their mother's size, and it matched her mane color too. Then they heard, "Children, what are you doing in here?"
They turned to see their mother. They knew she more then likely sensed their presence in here as she would scan their magical whereabouts every so often. "Well, we were curious of what was in this room. We didn't touch anything, honest," Moon Dust said.
"We were just looking around," Eclipse added.
Luna smiled, "Well, I think we've had enough site seeing for today and..."
Her sentence was cut short, as a gust of wind had slammed the door behind her. This had shaken the room so hard, relics began to topple over. Then something happened that Luna had tried to stop, but had reacted to late. One of the relics hit the lock on the chest that the little ones had been wary of. It was then the chest burst open and a dark sparkling mist erupted into the room. The three heard a sinister, yet feminine voice bellow, "HAHAHA! Finally, after all that time of waiting, I am free. It is time to set forth my plan that should have been set in motion long ago!"
The mist then turned to Luna and her children. "Ah. I thought I might find you here princess. We have much work to do," the voice said.
"You will not win me over this time you monster. Stay Away From Us!" Luna commanded as she shot a beam of magic.
The mist managed to dodge it. "Hmmm. You show much reluctance this time around. Perhaps it is time to find another. And young fillies and colts are too feeble, even if they are your alicorn decendants," the mist spoke.
Luna shot another beam, and this sent the mist to open the door and escape. Moon Dust and Eclipse trembled. "M-m-mommy, what was that thing? W-Why was she after you?" Moon Dust studdered.
Luna nuzzled her son and daughter and answered, "A Monster that I ran into in the past. One time it tricked me into being it's ally. But this time I must track it down and stand against it. Until we find it, I want you two to stay close to the Lunar chambers, alright. And you're not in trouble. This was not your fault, so don't think it is okay little ones?"
Her children nodded, and they soon trotted off with their Lunar cartaker back to the chambers, too frightened to want to try and pull any pranks at this time. Meanwhile Luna trotted back to the throne room where her fellow princesses, the element bearers, and Starlight Glimmer were waiting. As she entered she took a deep breath and stated, "Sister, I have frightening news."
"What is it my little sister?" Celestia inquired.
"There's no easy way to state this, but, the Nightmare Force is back. She's awakened and she's more fierce then ever," Luna said.
The whole group gasped, as did the guard ponies who had been standing by the throne and at the door entrance. "Silver Hoof, inform Shadow Comet of this as well as Shining Armor. Put all our guard on alert," Celestia commanded and Sliver Hoof gave a salute, soon taking action.