Dear [Insert],

Dear Sunset Shimmer,

We may not properly know each other due to my thousand-year exile but my sister has told me such wonderful things about you, believe me. Much like Twilight, she spoke so fondly of you; the lessons she had taught you but I could also feel a sense of remorse embedded within her words.

Forgive me but she has told me about where the two of you separated. While I don't blame you, I don't blame my sister either. Again, forgive me for my bluntness but you were in the wrong and so was my sister. We all have misunderstandings like the time I turned my back on my own sister, much like how you did with her.

My sister tends to... forget to acknowledge those who are important to her.

I see myself a lot within you, Sunset Shimmer, and this is why I have written to you. To have you be taught under my wing. I'll teach you everything your ambition wants you to know and I'll even help you channel your ambition.

Hopefully, you accept this gracious offer.

Yours Soon-To-Be Teacher,
Princess Luna of the Night

When Sunset took her gaze away from her journal, she closed the book closed and hugged it tight to her chest while also breathing a sigh.

''So, then, is that a yes or a no?'' Spike asked, standing next to her.

Sunset looked at him, nuzzling him in awe. ''Should I?''

''I think you should,'' he offered. ''That way you can rule the night over there while Twilight rules the day! You can both be the next sun and moon princesses!''

Sunset rolled her eyes and chuckled. ''I'm pretty sure I've learned to never let my ambition get ahold of me.''

She then turned to open her journal and glanced at the text.

I'll even help you to channel your ambition.

Sunset thought about it for a half-second before clicking her pen and writing her answer on the page.

I would gladly accept.

She sighed and brought herself and Spike to lay on the grass.

Twilight trotted back and forth, waiting for her friend to come through the mirror placed in front of her in her castle library. Soon, the mirror vibrated and had a yellow unicorn with a fiery mane come out of it.

''You're here!'' she exclaimed, coming forward to hug the unicorn. ''It's been so long. How have you been?''

Sunset used her friend to balance herself on two hooves before going on all fours.

''I've been better actually,'' she replied. ''What about you? How's princess life? Must be really special to be up there.''

Twilight's ears fell. ''About that,'' she said. ''I'll tell you later. Right now, Princess Luna wants you. It was so thoughtful of her to take you under her wing.''

''Yeah, but I'm also sorta nervous,'' Sunset said. ''What if I fail her just like I failed Celestia?''

''First of all, you never failed Celestia. You were just... misguided and angered. And I doubt you'll fail your next teacher after learning about friendship from the best teacher there is.'' Twilight winked her eyebrows at her.

Sunset pulled away from her. ''Anyway, let's get going.''

Twilight nodded and led her friend out the library's doors. ''You wouldn't mind if I teleport us there, do you?''

''Not at all,'' Sunset offered. ''Teleport the way!''

She smiled and closed her eyes, concentrating. A glow of magenta illuminated her horn, and in a spark of light, they disappeared from the library and reappeared in the Canterlot throne room.

''Whew. Haven't done that in a long time,'' said Sunset, glancing up to see who was in front of her. ''Uh, Twi? A little help here.''

Twilight got up from the ground and looked at the Princess of the Night herself.

''Luna, meet Sunset and Sunset, meet Luna.''

''Charm,'' Luna said, taking her hoof out.

Sunset merely stared at it, being nudged to place her hoof atop by Twilight. And then she did.

''My sister has told me so much about you,'' Luna began after an awkward silence. ''She said you've been doing well in that other world with Twilight's friends' counterparts.''

''Yes, I have,'' Sunset replied, turning to look at Twilight for support.

Luna noticed this. ''Twilight, I hate to have you be standing here doing nothing so you can go help my sister with her duties. She'll be in the other room.''

''Right. Of course.'' Twilight bowed before stepping out.

Luna turned to Sunset. ''We shall no need for formalities. I even informed Starlight Glimmer, maybe you've heard of her, to come and join us.''

''Twilight's student. Oh, I know who she is. Yeah, she's pretty dope.''

A knock occurred at the door before Luna could point out this new vocabulary she had not caught up with yet. She allowed the guards to open it and a lavender unicorn sheepishly walked in.

''Princess Luna,'' she said as she entered in, catching the sight of... ''Sunset Shimmer.''

''Hi Starlight,'' Sunset greeted, relieved. ''I'm so glad to have someone else with me along.''

Luna neatly tucked her wings away and began speaking: ''As you both probably know, I've decided to take you two under my wing much like how my sister did with your friend Twilight.''

Sunset put up her hoof. ''Twilight became an alicorn princess... will Starlight and I become too?''

''Perhaps,'' Luna offered. ''Perhaps, the two of you could take over our thrones one day but we don't want our hopes and ambitions up, do we?'' She eyed Sunset especially. ''After all, we're here to channel them.''

''Yes, Princess Luna,'' Sunset and Starlight both said in unison.

''Now,'' Luna said, ''we'll be meeting in pony whenever you need to take a test or there's a spell I want to teach you. You two will be sending me reports on the magic of friendship. Sound familiar?''

Starlight scratched her head. ''Twilight told me she did this with her mentor.''

''Mhm.'' Sunset nodded. ''I sent reports to Princess Celestia about magic, not friendship. I think reports on friendship started with Twilight.''

''Guess she really is special,'' Starlight mumbled as she chuckled alongside Sunset.

''That is all,'' Luna said as she put up her hoof and splayed out her wings to dismiss the two unicorns, the double doors opening in her magic to let the two out.

Over time, Sunset and Starlight would write letters back and forth much like how the former would with Twilight. Sunset and Starlight sent reports on the magic of friendship to their mentor Princess Luna as instructed.

Luna sat in her lounge, reading through scrolls sent to her by Starlight through Spike's fire breath and her sister's journal where she could contact Sunset.

Dear Princess Luna,

Today I learned that no matter how many times your Great and Powerful friend annoys you, you should never, ever, EVER pour your anger out on them as it will break apart the friendship and make matters worse.

Your Student,
Starlight Glimmer

P.S. Trixie wants to be your student too.

P.S.S. Or Celestia's, she doesn't mind being equal with Twilight. Speaking of Twilight, she told me to sign myself as 'Your Faithful Student' every time I send you a letter. No idea why.

Okay, so I was at the school's faculty lot when Snips and Snails started drinking beer there and your counterpart came out but they ran away to avoid getting caught. She had a good sense of smell where she was able to make out the smell of beer in the air.

She brought everyone in that she noticed were in the faculty lot and tried getting us to tell her who did it.

Applejack and I wanted to tell her the truth but Rarity told us not to as she didn't want us to be dragged into Snips and Snails' situation. But being honest will quicken things. Twilight even backed Rarity up with some 'scientifical points'. You know how it goes.

But eventually, Applejack and I told Vice Principal Luna the truth. I guess the lesson here is to always be honest?

Yeah, no.

Your Student,
Sunset Shimmer

Luna tore her gaze away from the journal and parchment and looked out the window where her sister was lowering the sun below the horizon which got her to realize it was her turn to bring up her night now, and so she did. She lightened up her horn and closed her eyes, concentrating. Slowly, the moon began to rise over the skyline, stars peeking through the dark sky.