**ZZAAAAPP**
The foul corrupting blast from King Sombra slammed into the wall above Luna's head. It had just missed Celestia by just a hair causing Luna to leap behind a crystal shard to gain cover. This was not what the sisters were expecting when they came to the Crystal Empire. They had arrived just a few hours ago and they found a unicorn powerful enough to hold off their new power. How was that possible? Where was he getting his power?
Another blast took out the top of the crystal shard Luna hid behind as she was lost in her thoughts. She quickly dodged the falling piece trying her best to figure out his weakness. So far every spell tossed at him was met with a black shard blocking it or simply dodged with a laugh. And each spell only seemed to fuel his power. She slammed into the window ledge getting a view of the crystal ponies in chains below. Chains leading to the castle. A sudden moment of realization came to Luna. The once powerful kingdom which survived by love and light lay dark and hateful before her. THAT WAS IT! That was how he was so powerful. He was fueled by the negativity and hopelessness of the crystal ponies! Where before the Kingdom gained the power it was all being directed to him.
Of course now that she knew that, how was she supposed to break that bond? I mean those ponies were subjected to soul crushing slavery for years. How was she supposed to dispel that? How were they supposed to break that kind of hold? It fueled his power of hate and...darkness. DARKNESS! If his power focused on that then they needed light, but Celestia would need an immense amount of power to cast a spell strong enough. They had one shot at this.
Another thought entered Luna's mind at that point. She remembered how the light and dark when she looked out the window seemed to be locked in battle. Luna got her powers from the darkness as well. Which meant she was just like King Sombra. A being of darkness. A being that could not survive in the light. Luna looked out at the enslaved ponies and their hopeless expressions. Was she like this?
A cry came from Celestia at that time and Luna shook her head and turned back to the battle and gasped. Sombra had gained an upper hand over Celestia and had her pinned in a corner. Celestia had a barrier up but was obviously struggling to keep the assault at bay. Luna raced over launching a spell looking like a lightning strike towards him causing him to stop attacking Celestia and quickly dodge out of its way. Luna quickly went over to her sister and took a sturdy and protective stance in front of her. But the doubt on her face showed through. Sombra noticed and smiled wickedly.
"Sister! His power comes from the darkness clouding the crystal ponies hearts! You must dispel the bond with a strong surge of light and cast it into the bond he has over them. That should weaken him long enough to defeat him. Quickly now! I will distract him while you gather the necessary power!" Luna explained in a loud voice. A look of fear crossed Sombra's face before he renewed his attack.
Celestia nodded and closed her eyes. First she needed to cast the spell to be able to see the bond. When she opened her eyes again they glowed in a golden hue and she saw the black, hideous, and revolting tendrils cascading off Sombra. The scene was surreal. Sombra actually looked like a mass of darkness not a unicorn anymore. But with this vision she also saw where he had attached the tendrils. His black heart. It was almost too much even to look at, black as night and more foul than anything she had seen before. Celestia started gathering power into her horn. Her pink mane started to shimmer in multiple hues slightly as she did.
Luna flew straight at Sombra, launching ray after crackling ray of bright light at him. The doubts swarming in her mind as she stalled to give her sister time. Sombra dodged ray after ray his wicked smile growing at the sight of Luna's doubt. Luna's own mane started to darken and shimmer with small pinpricks of light as she cast spell after spell.
"Is there a problem, Miss Alicorn of the Night? I would think you and I would be allies here," Sombra hissed watching as his comment drove the doubt deeper into Luna's mind. If he could turn this one against her sister he would have a much easier time with this battle. As he felt smug about this idea he heard a light ringing noise and looked past the Night Alicorn and saw the large amount of stored power in Celestia's horn and panic shot through him for a second.
Then a thought occurred to him and he smiled and turned back to Luna. He only needed to get this one to tell her to stop, "Oh dear, it would appear the Alicorn of the Light is going to cast a rather nasty spell for beings such as us," whispered Sombra, his manic glee rising as he saw Luna look at her sister and gulp down her fear. "Certainly you do not wish to be hit by such a blast being a creature of the night and all. Honestly I also wonder why you fight me. Does anyone even appreciate your talent or do they simply shun it?" He hissed wickedly again. The result of his words actually surprised him.
Luna stopped. Hovering in front of Sombra in shock. She suddenly remembered how when she had first brought on the night, the ponies had stopped celebrating. Ever since the sun had been put in the sky right after Discord's defeat they had celebrated. When Luna brought on the night they stopped they did not offer up the praises her sister had gotten, they did not praise the moon. No they simply ignored it and went to sleep. Like she did not matter. Luna suddenly gathered a large amount of power into her horn ready to strike the source of this realization down, her face contorted in anger. Sombra recoiled slightly suddenly regretting his words.
Not hearing a word of the conversation, Celestia saw Luna stop and she became worried that Luna had been hurt or worse, affected by a dark spell that was warping her mind. She failed to notice the dark swirls in Luna's heart with her vision. When Luna gathered so much power into her horn Celestia smiled. She knew she had not gathered enough power and it would take too long to gather enough on her own but if she linked herself to Luna's power they had more than enough together. Celestia smiled at the thought of again defeating a foe with her sister. She launched her spell at Luna hitting her horn.
Luna was about to release her spell when she felt Celestia's magic hit her horn. She felt it fill her with power then her sister's voice came into her mind.
"Quickly sister, I have given you the power I have stored up. We must use our combined powers to defeat him! I will aim the spell. When I say to release the power then you need to push it out!" Luna hung in the air, she felt odd. The power was overwhelming. It flowed through and around her. Sombra was in shock at the site. Then Celestia spoke in Luna's mind again. "Now! Release the power!" This whole ordeal lasted only the briefest of seconds, Luna pushed out the power as instructed and as it hit Sombra his mortal shell seemed to melt away. But the bond was not destroyed instead Sombra became the bond and Celestia and Luna were shocked to see him become shadow.
Luna quickly redirected the magic to push Sombra out of the castle and towards the North. The tendrils followed to the horror of Celestia. Luna slammed the dark form of Sombra into a glacier and then formed one of the most complex seals Celestia had seen in a long time. And Sombra roared in anger and then smiled at Luna.
He opened his mouth to speak but while Celestia was busy trying to understand the seal Luna had made. Luna slammed a bit of the magic down Sombra's open mouth and heard him gag and cough. That was enough of his words for today.
Luna continued working the seal and was about to finish it when Sombra pushed a wave of power into the tendrils. The whole empire wavered from view. Luna locked the seal but not before Sombra pushed one more blast of power and the Empire faded as Sombra hoarsely laughed at his final trick. The Alicorns may have won the battle against him. But they failed in their goal to save the Empire. He would return to once again claim his precious crystal slaves!
The Crystal Empire was gone. Luna and Celestia hung in the air in shock. Where the beautiful castle once stood and pushed back the harsh cold north wind. Nothing stood. Luna landed and tears formed as she felt the doubts cloud her mind. They were now much stronger. Why did the ponies shun her? Did they see her in the same way as Sombra? A dark presence? Celestia mistook the tears on Luna's face for regret at not freeing the crystal ponies. And was about to comfort her sister when Luna collapsed into the snow and sobbed loudly.
Celestia started to approach her sister when a message came out of her horn. It demanded she come back as soon as possible the unicorn nobles were trying to rule in her stead and a revolution was in the works. Celestia decided to let her sister have some time and went back to Canterlot by wing. Luna heard her sister leave and picked the note up in her magic. pulling it over she read it and only thought about how there was no mention or asking about her. They only recognized Celestia as their Princess it seemed.