A sky blue pegasus walked down the long corridor to the throne room where she was summoned. Her mechanical wing clanked against her armor as she walked. To her right were a series of stained glass windows. Each depicted a different scene. Some were of happier times. Others showed past wars. She walked up to one and stopped. It showed a lavender colored Alicon battling with King Sombra. In the bottom of the window showed the fallen Alicorn with King Sombra standing over her.
“....Twilight, why did you do it?” She allowed herself of moment of weakness as a single tear rolled down her cheek. She lifted her right hoof and placed it on the stain glass window and bowed her head. After a few moments she regain her composure and continued down the corridor.
In front of her were two large wooden doors, beyond them held her destination. The two guards saluted her as they opened the door to allow her entry. The doors lead into a grand hall with vaulted ceilings. Even in war time the staff kept the place sparkling. Sitting upon one of the thrones was a swan like Alicorn, standing next to her was a smaller pegasus with bright orange and yellow hair wearing a pair of aviator sunglasses.
“Ahh Commander Dash, so nice of you to join us.”
“It’s not like I had much of a choice, General Spitfire. What is it you and the Princess wish to speak to me about?” Rainbow Dash looked up at the Alicorn sitting on her throne.
“Tell me, why did you join the Air Corp?”
“To protect Equestria from those who wish us harm.” Rainbow Dash was a little puzzled by the question but she didn’t let it show.
“And how far would you go to ensure that safety?”
“As far as I need to even if I end up in Tartarus for my actions.” Celestia started to chuckle a little bit.
“Well you won't need to go that far this time. You and Pinkamena have been chosen to travel to a separate timeline to seek out intel on how they were able to defeat King Sombra. When you get there seek out that timeline’s Celestia she will aid you in your mission. For where you are going I can not help you. You and Pinkamena are going to be on your own. Remember your presents must remain as unnoticed as possible. One last thing before you go. Time is not on our side.”
“Yes Princess, I shall prepare for departure immediately.” Rainbow Dash turned around and walked out of the hall. Rarity isn’t going to like this at all.
“YOUR WHAT!?” Rarity’s eyes went wide in shock.
“I’m being sent away on a mission, I’m not allowed any contact to anypony and I don’t know how long I’ll be gone.” Rainbow Dash felt her heart sink when Rarity started to cry. It pained the sky blue pegasus to see her hurt.
“But, but -sniffle- where are you going? Why can’t I write you?” Rarity mascara started to run down her pale white cheeks.
“I’m sorry Love but I can’t answer those questions. I know this hard, but we knew this might happen at some point. All I ask is for you to stand by me and wait this out.” Rainbow Dash moved forward to hold Rarity but was met with a hoof to the chest.
“I SWEAR to Celestia that if you come home in a pine box I’ll go to Tartarus myself to kick your ass. I don’t need my Dashie to come home missing anymore pieces. Now if you’ll excuse me I must go and fix my mascara before we leave for dinner. At least I get one last night with you before you leave.”
As Rarity walked away Rainbow Dash tried to open her mouth. But she didn’t have the heart to tell her she would be leaving after dinner. She’d let Rarity have her fantasy for the time being.
“Rainbow Darling where are we going anyway?”
“I’m not telling you. You’ll find out when we get there.” Rarity walked out of the back of the house pouting. “Come on sweetie we’re going to be late.”
“I told you I’ll be fine. It’s not like this is the first time I’ll be going a length of time without you.”
“Maud, I know how you get.” Pinkamena stared at her sister trying to read her face. To anypony else Maud never gave off facial expressions, but to Pinkamena it was the gateway to her sister's inner thoughts.
“Look, I can take care of myself and I can handle running our battalion. You need to focus on your mission at hand. Don’t worry about me.”
“That's a stupid thing to say to your sister. Even after we lost both Limestone and Marble to this war.” Pinkamena pulled her sister in for a hug. After a few moments she pulled away. “I’m going to double check that I got everything I need. Then I need to go get Rainbow Dash.”
Later that evening Pinkamena walked into the restaurant that Rarity and Rainbow Dash were at. She scanned the room for the pegasus she was looking for. They were sitting at a table in the back. A hostess walked up to her.
“Are we eating alone tonight are waiting for a party?”
“Neither, I’m picking somepony up.” Pinkamena pushed past the hostess and walked toward Rarity and Rainbow Dash. Rarity caught sight of her first.
“Pinkamena, it’s so nice to see you. How are you doing tonight?”
“Hello Rarity, but you’re not going to like me right now. Commander Dash we need to go.” Rainbow Dash sighed aloud.
“Can’t you see I’m in the middle of something?”
“Our orders have changed, we leave now.” Rarity’s ears fell to the side of her head as her expression changed. Tears started to swell up in her blue eyes.
“But.....you said you didn’t leave until tomorrow morning. Dashie what's going on?”
“Higher ups have changed their minds I guess.” Rainbow Dash stood up and walked over to Rarity. “I love you, I hope you know that. I want you to have this, just in case I don’t come back. Just so you know how much you mean to me.”
She kissed Rarity softly on her lips then handed her a small box.
“Wait until you get home if you're going to open it. The choice is your however if you even want to open it.”
“Dashie......is, is it what I think it is? You ruffenant don’t talk like that. You are going to come home to me!” The look in her eyes was one of pain and anger. “I’ll give you a reason too because my answer is yes.” The alabaster mare lept forward and wrapped her legs around her lover's neck.
“Commander we need to get going.”
The two shared a heated kiss before separating.
“I love you darling.”
“I love you too Rarity.”
Rainbow Dash and Pinkamena turned around and walked away from the table. Once they got outside Pinkamena looked over at Rainbow Dash.
“Why don’t you just tell her the truth?”
“I wanted to see her happy before I left. It breaks her heart when she knows I have to leave immediately.” Pinkamena rolled her eyes at Rainbow Dash and snorted. “Oh shut up, come on we’re going to be late.”
Author's Note
There's a lot of back story here. Next Chapter Pinkie Pie meets Pinkamena. 
(maybe) lol
