The Lonely Mare
Celestia stood there, feeling useless as she watched the love of her life, Sombra, use the Elements of Harmony to absorb the dark magic from the other Celestia and Luna. When he was done, and the Elements of Harmony returned to Twilight and her friends, Celestia approached Sombra slowly and stretched her right foreleg to his shoulder.
"S-Sombra?" Just when she touched him, he turned around, growling like a monster. Her only true love had turned into something monstrous and evil.
"No! No!" Celestia backed away slowly, tears streaming from her eyes. The world around her began to melt, everything was melting except for the corrupted Sombra. Soon, there was nothing around her but darkness and Sombra approaching her slowly, his eyes shooting her a fiery, monstrous glare, burning her soul and eating her heart.
"No! Please, Sombra! Come back to me!" Celestia pleaded through her loud sobbing, but there were no replies except for growls that kept getting louder, adding to the wreckage of Celestia's heart.
"No, no! Don't do this! Please!" Celestia's tears became almost waterfalls, but Sombra just kept growling and trotting towards her. In the end, he pounced at her, and she saw no more.
Celestia opened her teary eyes and sat up slowly in her bed. She wiped her tears and sighed sadly. Ever since she returned from the alternate Equestria and lost her only true love, she had been frequently getting those nightmares that only added to her growing sadness. She had told Twilight back then that she would get better with time, but she was so wrong. How can you forget your true love? How can you get over the most painful heartbreak in your life? If anything, she had gotten worse with time. She had learned that time can't heal everything. But she had never let anypony notice her sadness and never let it affect her duties. Even if her heart had been being crushed all over again with every nightmare and every time she stared at the mirror piece that she had kept hanging on the branch of a little tree in the window of her bedroom.
She slid from her bed and trotted slowly to the window, "I can't forget you, Sombra. And that's killing me," she whispered to herself. She opened the window magically but didn't glance at the mirror piece on the small tree branch so she wouldn't lose her concentration on the dark horizon with her horn still aglow, and few moments later, the sun rose high, announcing the beginning of a new day. A new day of her tortuous loneliness. It's true that she had her sister and a lot of friends, but even that can't heal the scar caused by losing Sombra. Even her whole castle with its stunning wideness felt like a prison cell whenever she remembered the moment she lost him.
Celestia kept trotting towards the window and staring at the mirror piece, while she quietly sang a sad song she had made to mourn her own state:
Am I destined to stay alone forever?
I'm all alone with no love to shield me
With every morning I hope I'll become better
Only to find sadness further tearing inside me
Every time I open my door
I'm met with sorrow I can't ignore
Is it my fate to stay alone?
Is it my fate to love no more?
It's my dream to meet my love once more
To ask him and heal my heart's sore...
Celestia picked the mirror piece with her magic and placed it in her right foreleg, staring at her reflection as she let tears trickle on the piece,
...Will you be my mirror? Forever more?
Celestia finished singing and rested her head at the window frame beside the small tree, sobbing quietly, "Oh, Sombra! I'll never see you again."
Celestia shot upwards and immediately hid the mirror piece under her folded right wing, as her bedroom's door flew open, revealing a smiling-from-ear-to-ear Luna.
"TIA!" Luna exclaimed cheerfully.
"Luna? Wh..." Celestia couldn't finish her statement, as her younger sister threw her body at her, pinning her to the ground with a tight embrace.
"Good morning, Tia!" Luna loosened her embrace and stood up. She saw the tears on her sister's cheeks and wiped a tear with her right foreleg, "What's this? Are you okay, sister?"
Celestia stood up and took a few steps back while wiping her tears, "No, no, no! It's nothing. It's just, when I opened the window to raise the sun, something stuck in my eye and it was very hard to take it out. Now, may I ask you why the...extreme cheerfulness and excitement? Not to mention that you entered my room without knocking on the door."
The Princess of the Night jumped in her place and spoke quickly, "I'm just so excited, and you should be so excited, too!"
"Luna, you're acting like Pinkie Pie!"
Luna stopped jumping and smiled sheepishly, "Hehe! Sorry. It's just, I can't wait to show you the surprise!"
Celestia raised an eyebrow, "Surprise? What surprise?"
"I can't tell you, because it's a surprise! But believe me, you can never guess what it is! Now come on, let's go and show you your morning surprise!" Luna turned to the door to leave.
"Okay. Just let me have a breakfast." Celestia trotted slowly to the door.
"Aahhh! There's no time for breakfast! Come on!" Luna took her sister by surprise, as she grabbed her right foreleg in hers and dragged her out of the room, "Just take your teacup and come with me!" Luna left her sister in the front of a servant carrying a trey with a cup of tea on top off it, then galloped away.
Celestia blinked in confusion. It's not everyday she sees her sister acting so Pinkie-like. She took the cup of tea magically, took a sip from it, and hurried behind her younger sister, with the teacup still in her magic grasp.
She followed her to the room where Starswirl The Bearded's scrolls were kept, still having no idea why her sister was so excited and why she herself should be excited. She entered the room slowly, still carrying the teacup, "I just can't guess what would be so important that I must see before I have my...breakfast." Celestia froze in her place and dropped the empty teacup to the floor, staring in utter shock and surprise at the scene in front of her.
Standing there were Twilight and all her friends with a big mirror in the middle. But that wasn't any mirror. It was the mirror she had used to travel to the alternate Equestria where she met Sombra. But the mirror still missed a little piece of glass.
"SURPRISE!" everyone in the room, including Luna, cheered loudly.
Celestia couldn't talk. She just trotted slowly towards them with her eyes opened widely and her mouth agape.
"What do you think, sister?" Luna asked, but there was no reply.
Twilight stepped forward to speak, "Princess, remember when you asked us to destroy the remains of this mirror? Well, we didn't. I kept the remains and since that day, I've been working on rebuilding the mirror. I made a lot of studies and discovered that the paradoxes were caused by the mirror itself, not your relationship with Sombra. So, I took all Starswirl's scrolls about it and modified some spells to make the mirror safe. Now, there will be no more paradoxes! We can travel between the two Equestrias as many times as we want. No matter what happens in here, it won't affect there, and vice versa."
"Twilight has been working SO hard!" Spike said, "Some days, she hasn't even slept, just to fix this mirror."
"We all helped and supported her," Rainbow Dash said.
"Especially in reassembling the mirror pieces," Applejack said.
"Just for you, Princess!" Pinkie said.
"We just couldn't stand thinking about the sadness you had to go through, so we made this," Fluttershy said.
"I would do anything to help reunite two, separated lovers. Especially if one of these lovers is our Princess," Rarity added.
Celestia approached Twilight and hugged her so tightly, and Twilight returned the embrace, feeling the tears dropping on her head.
"Thank you so SO much, Twilight!" Celestia said in her crying, still hugging Twilight, "You're the best student any mentor can ever dream of!"
"And you're the best mentor, Princess. That's why we made this for you," Twilight replied.
Celestia broke the embrace and gazed at everyone with a tearful smile, "Thank you. All of you. I just...I can't believe you did this just for me!"
"This is the least thing we can do for our beloved Princess," Applejack said.
"I couldn't stand seeing your sadness grow with time, sister," Luna spoke, stepping beside her elder sister.
"What? But I made sure no pony would notice that," Celestia replied.
"Are you kidding?! I'm your sister! I couldn't bear watching you mourning your state ever since we returned from the other Equestria. And I have to say that my heart broke when I heard your sad song just few minutes ago..."
Luna trotted to her sister's bedroom's door with a wide smile on her face. But her smile faded once she heard the heartbreaking singing of her sister from the inside.
"...Will you be my mirror? Forever more?"
A stray tear trickled down on Luna's cheek, but she wiped it quickly and forced her ear-to-ear smile, before she stormed inside the room.
End of Flashback
"Oh...I...I'm sorry you had to hear that," Celestia said, blushing lightly and trying to hide her face.
"Ah, that's okay. Your voice wasn't bad," Luna joked, causing everyone to laugh.
A warm smile crept to Celestia's face.
"Now, the mirror needs jut one more piece to be complete," Twilight said, pointing at the empty spot in the mirror's glass.
"You know what piece this is, don't you, Tia?" Luna asked, fully knowing what the missing piece was.
Celestia widened her eyes and unfolded her right wing, causing the mirror piece to fall. But she grabbed the piece with her magic before it hit the floor. She placed it in her right foreleg and approached the mirror slowly. Taking a last glance at everyone around her, and receiving nodding, she placed the mirror piece in its place. When she retracted her hoof, a slight golden glow happened at the edges of the piece, and when the glow disappeared, the edges were smoothed, the mirror seemed new as if it had never been broken, and Celestia hoped that the same thing will happen to her heart very soon, until she remembered something.
"But, Twilight, don't you remember that Sombra has absorbed dark magic? He's evil and very dangerous right now," Celestia said.
"Eeyup! And we're more than ready to change that," Applejack said confidently.
"We're not the Elements of Harmony for nothing," Twilight said, a confidant smile on her face.
"Rainbow Power, oh yeah!" Rainbow Dash added.
Celestia was even more surprised, "Y-you're going to do this? You're going to put yourselves in danger, just for me?!"
"We volunteer to do that, Princess," Twilight replied, "And we won't accept a 'No' for an answer. We're gonna go there, cure Sombra and you can do nothing to stop us!"
"You did a lot of things for the sake of others in your life, not to mention raising the sun everyday, and you deserve something to be done for your sake. That's the least thing we can give you to express how much we're thankful," Applejack said.
More tears of joy flooded Celestia's eyes at that moment, "I...I can't let you put yourselves..."
"Princess! We're gonna fix Sombra. Are you coming with us or not?" Twilight said firmly.
Celestia smiled and nodded, "Thank you. I can never thank you enough for doing this."
"You don't have to, Princess," Rainbow Dash spoke up, "Doing this mission is how we are saying 'Thanks' to you."
"Go with them, Tia. I'll take care of everything in your absence," Luna said.
"But, we may be gone for days. Are you sure?" Celestia asked.
"Never been more sure before."
"Even raising the sun? I mean, it's hard for you..."
"Thou shalt accept our offer!" Luna yelled jokingly.
Celestia giggled, "Thank you, Luna."
"Thou do not have to thank us," Luna replied, causing Celestia to giggle more.
"Now, let's see..." Twilight said, levitating a big scroll with her magic. A Few moments later, her horn glowed brightly, along with the mirror. Then, the gems at the mirror's frame began to glow while the mirror itself stopped glowing but vibrated like a liquid surface, "Ha! YES! It worked! It worked just like I planned it! Everypony, are you ready?"
"Sure we are!" Applejcak replied.
"Let's begin our new adventure!" Rainbow Dash exclaimed excitedly.
"Sure there's going to be a lot of dirt, but it's worth it," Rarity said.
"After you, Princess," Twilight said, stepping aside from the mirror to allow Celestia to pass first.
Celestia approached the mirror slowly and stood in front of it. She took a last glance behind at her sister, "Take care of yourself, Luna."
"You're the one who should take care of herself! I'm just staying here while you are adventuring to an alternate universe!" Luna replied.
Celestia chuckled. She turned to the mirror and took a deep breath while staring at her reflection in the liquid-like surface of the mirror, "Sombra, here I come. Our suffering shall end soon." With that, Celestia stepped to the other side, with Twilight and her friends following behind.
Let the adventure to reunite the royal lovers begin.