After being told what she had witnessed and finding what Twilight was doing with the other princesses along with Pinkie Pie, Celestia was beyond mortified. She had always thought that Twilight, Pinkie, Cadence, and Luna were hiding something from her, but she could not have ever imagined the four of them experiment on the dark essence of the Corruption. As she was thinking about what to do, Starlight asked,

"What are we gonna do, Princess? Twilight, Pinkie, and the other two princesses believe this will help fight back against the Anomaly, but if this gets out of hand, Equestria will be destroyed or worse!"

Celestia was still deep in thought about what they were going do next.

"Princess?" Starlight asked.

"I appreciate all that you have done for me, Starlight Glimmer." Celestia said.

"What are you talking about?" Starlight asked as tears slowly started pouring out again.

"Even after all the horrible things that have happened to Equestria and seeing Twilight and her friends go against everything that I stood for as their teacher, you were the only one who stood behind the Principles of Friendship. I could never have been more proud of you than I already am."

"P-Princess? You're not planning on-"

"No. I am just going to talk to them. I am not going anywhere." Celestia assured.

Starlight knew right away that it was a lie, but said nothing.

"I will see to this matter myself. You may go." Celestia said as she headed towards the door.

With that said, Celestia left her room and Starlight was left to worry about what would happen next.

"What have I done..." Starlight said with tears pouring out of her eyes.

***

Making her way towards the castle, the guards attempted to stop her.

"P-Princess, we don't believe it's the best time to-"

Before they could speak any further, Celestia moved them aside and proceeded to head towards the throne room. The other three alicorns were inside.

"Good evening, ladies. How goes the cause?" Celestia asked in a sarcastic manner.

"Sister...?" Luna asked.

"Ah. How long has it been since the four of us have been together like this. Makes me feel like we're back in Canterlot when Twilight finally became the Princess of Friendship. Isn't it quite nostalgic?"

"Celestia... please-" Cadence said before being interrupted by Celestia.

"But it seems that those day are now long behind us. Due to all the Corruption surrounding us, it seems unlikely that there will be an unlikely chance that we will be celebrating. Right, Twilight?" Celestia asked, looking directly at Twilight.

"I have no idea what you're trying to do Celestia, but it won't work." Twilight said, feeling annoyed.

"What won't work?" Celestia asked in a clueless manner.

"The idea of you trying to figure out what we're planning. Right now, you are all that's keeping our spirits up. So for your own good, please-"

"For my own good? I thought I was the Sun Princess?"

"Sister..." Luna said.

"A little birdie told me that you were taking something inside the Crystal Empire. Said it looked like the same ooze that has corrupted Equestria. Care to show me this ooze?" Celestia asked, now looking at Twilight's bag.

The girls were now nervous as they now know that Celestia is aware of the ooze.

"Sister, I don't think-"

"Please, I insist. It would be our little secret."

"Princess... I think it would be for the best if you returned to your room." Twilight warned.

"Is that a threat, I hear? I just wanted to see since we're all princess. Are we not princesses?"

"Celestia, we're planning something right now and we need focus if we want this to succeed."

"Then how do you explain this?" Celestia asked, levitating the canister out of Twilight's bag.

Everypony was shocked to see that Celestia knew all along that they were hiding the ooze. Now knowing that they were keeping this all a secret from, Celestia was angrier more than ever.

"Sister... I know that this is quite a shock to you, but-"

"But what? We were having some fun catching up with each other." Celestia said.

"I think you should leave now, Princess." Twilight said with angry undertones.

"You know what I think, Twilight? I think you are out of your mind for bringing this inside the Crystal Empire." Celestia said, starting to get angry.

"Celestia, we have run out of options. If we don't do something about this-"

"Then what? We lose everypony here? Please tell me that was a joke, Cadence. Because I missed the point of it!"

"Sister, many are dying and unless we study on this ooze, we will lose more by everyday's end."

"Don't worry, Princess. We are doing completely fine without you." Twilight said in a condescending manner.

"And this is what you qualify as fine?! Holding secret meetings without me?! Risking the lives of everypony in the Crystal Empire?! I can't believe you are stooping to bringing in the very same essence that destroyed our kingdom!" Celestia shouted.

"Sister, we don't have any other choice left! We chose to keep this a secret from you because we already knew you would object to this! And it seems you have proved our suspicions correct." Luna said.

"I guess you haven't really changed much from after Twilight saved you from Nightmare Moon, sister." Celestia said with a scowl on her face.

"Sister...!"

Celestia turned towards Cadence and said,

"Have you forgotten that it was I who helped you get married in Canterlot before Chrysalis took over?"

"Celestia, we-"

"And you! I taught you everything I knew! I made you my apprentice because I knew within my heart that you would spread the lesson of Friendship far and wide from beyond Equestria! How could you have twisted and mangled all that I have taught you?! Using your friends to benefit your very needs and to see the ends of your own agenda! You were supposed to be the one different from all my other apprentices!!!" Celestia yelled with tears in her eyes.

Celestia turned her head away from the others as she headed for the door. But before she could leave, Luna stopped her and said,

"Sister..."

Celestia turned towards Luna and said in a tearful manner,

"I thought we were sisters..."

Hearing this shattered Luna's heart entirely as Celestia exited the throne room with her nerve. Twilight looked onwards in disappointment while Cadence felt worried about what would happen next.

***

After Celestia left the throne room, Twilight stops her and says,

“You know I’m right about this. If we don’t do something about this, Equestria will be in even greater danger than you know. Besides… someone got to act and it's clearly not you…”

Celestia stopped and turned towards Twilight. Few seconds later, she slaps Twilight in the face, shocking the two Alicorn Princesses.

“I can’t believe I ever made you my faithful student. Everything I taught you… everything I entrusted… wasted when you banished him. I thought you were different from all my other apprentices. But apparently, I was wrong.” Celestia said in an upset manner.

Twilight was surprised by her sudden action but at the same time, had no emotion to what just happened. “If you leave, you'll only be proving me right.” she said coldly.

Having heard enough of Twilight’s cold behavior, Celestia storms out of the castle and leaves the Crystal Empire.

As Celestia left, Starlight was hiding behind the doorway. Having listened in on the entire conversation, she was incredibly heartbroken to hear that Celestia was finally leaving the war. The girls were not sure about what would happen next now that Celestia left, but they knew that they had to keep doing what they can to further their studies on this black ooze and to see if they can find out ways to use it as a weapon against the Corruption.