A door that badly needed to be oiled crack open for the first time in years. Celestia step into a room she had ordered lock and no one enter till she allowed it. The room is a bedroom that was as she last seen it, the maids had clean up the room before the room was lock shut. The bedroom is that of her former student Sunset Shimmer when she was living in the castle. And the one who took away Twilight Sparkle.
She had the guards search for them, following every rumor about sightings of them. Before the mirror portal closed for another 30 moons she personally went to the other world with an escort much to the surprise of her human counterpart. They had no idea where Sunset is either and while there was a Twilight in that world it wasn't her Twilight.
They did discover where Sunset had lived while in the human world. A old store building that's been abandon for years. Sunset had been living in the old office room which from its state and repairs done to it was the only home Sunset knew in that world. There was power but it came from a extension cord that was connected to a nearby building. And what few belongings she own showed how she lived and how she survived in the human world. She collected cans and bottles to make money as well as stealing to survive. Something she was already use to before Celestia found her.
Celestia look around the bedroom covered in dust, remembering the past. She remembered the little filly that use to run around in the room and the look of joy when she was shown her room for the first time. She was living in the streets when Celestia discover her after she started that huge blaze when she wanted to stay warm for the night. She never seen someone with that much raw power and she took her in as her student. She train her so that when the time came she'll be able to free her sister from the evil that bound her. But Sunset only had eyes on her and didn't made any friends, instead she only wanted to be with her. Celestia realized that Sunset only wanted her attention and none other. It was by sheer chance that Twilight magic revealed to be as powerful as Sunset.
After she caught Sunset learning dark magic she replaced her with Twilight who unlike Sunset already had a family. She planned on keeping an eye on Sunset but she escape into the mirror. Learning from her mistakes with Sunset she began training Twilight into becoming the one who will free her sister from the evil that has her in its grips. But Twilight also came with her own problems and rather study then make friends. It was just blind luck things work out as well as it did. If Sunset was still around at the time she would have been her backup incase Twilight failed.
Now both of her students are gone. Both leaving letters to her, with Twilight leaving letters to her friends and family. Now the greatest defense for Equestria is now gone. Without the bearer of magic the other elements are useless. She is now searching for a replacement for Twilight. She remembered a talented unicorn name Trixie but she became a stage pony instead and after a show in Ponyvile she just disappeared.
"Sister?" Luna ask entering the room.
"I lost both of them," Celestia said. "I had such high hopes for both of them."
"Playing the trickster and stealth mentor has backfired on you. Hiding things and sending Twilight to handle things with no help at all. It's surprising it took her so long to see it," Luna said.
"I was only doing what I had to do to free you," Celestia said.
"Yes and I am grateful for it. But all of you manipulations that you have done to both of them. I know what you wanted to happen with Twilight and with Sunset before her. But that wasn't how either of us became alicorns. Now both of them are gone," Luna said.
"And with Cadence calling off the wedding till Twilight returns. There is no hope unless either of us marries, to see if one can be born as one," Celestia said.
"Her friends and family are still looking for Twilight. So you mustn't give up hope," Luna said.
"I know but without her. The elements are now powerless and the Changelings are still out there along with others. I going to take in another student and I won't make the same mistakes that cost me both Sunset and Twilight," Celestia said.
"Taking in another student already?" Luna ask.
"It's been more then a year and still no signs and if they're in the human world it be years till the mirror opens again," Celestia said.
"Remember dear sister of what you done to drive both of them away. Or you'll be seeing the next one leave your side as well," Luna said.
"I know but after watching so many dear friends and love ones, I knew from foal to old age come and go. Neither of us can afford to feel as our ponies do," Celestia said sadly. (1)
"I know sister," Luna said as she and her sister will outlive so many till they to will finally die.