Luna sat at her desk, staring into the depths of her coffee. It was strong and black, like the depths of the night sky, yet it didn’t hold the answers she hoped for. The blinds were shut in her office, the lights dimmed almost to non-existence, and the conversation played in her head on repeat. She didn’t even try to stop it—the entire thing had horrified her beyond measure, and it had taken every ounce of strength to not cry with the teen in her office as the story of her childhood came pouring out.

Blue-green eyes looked into hers, only half seeing her. “…She was my mom, in every way that mattered…except the one I wanted the most…” There was so much hurt in that one sentence, Luna couldn’t help herself; she reached out and squeezed Sunset’s hands between her own.

“She’s the earliest pony I remember—my oldest memory is waking up under her wing, being so warm and safe there, and following her out onto the balcony to watch her raise the sun and lower the moon. It was a little ritual for us for years, at sunrise and sunset. When I was too young to be left alone—my magic surges were violent and sudden until I was six or so—I played next to her throne in the throne room, or slept on her back between her wings. We’d eat lunch in the gardens, having picnics for just us, and sometimes she’d manage to get out of duties at dinner time, and we’d eat in her private dining room. I learned history at the same time I learned to read—in her study at night before bed, usually over dessert. She’d tell me stories from our history, and when I was older, she’d make me read the books aloud before she’d tell me what really happened."

“When I got sick, she made sure the palace doctors looked after me, that I got the best care. I remember this one time, I had…” she paused, then sniffled. “It doesn’t translate. Think the stomach flu and the chicken pox rolled into one—there’s no cure, you just have to ride it out and drink lots of fluids. I was so ill, I couldn’t keep anything down other than the tea she made me. Every time I had to throw up, she’d just…hold me in her magic, keep my mane back from my face. ‘Let it all out, little sun,’ she kept saying. I was…four? Maybe? She’d sing me to sleep too, when I was sick or scared or just couldn’t sleep…a lullaby just for me and no one else.”

Sunset took the tissues Luna presented her with, and blew her nose. “She was the closest thing to a mother I had. I was going to tell her once, but when I was looking for her, somepony reminded me that she wasn’t my mom. She was the Princess, and I was her ward, her student, not her child. As a foundling, an orphan, I was property of the state until the age of majority—it was her duty to look after me."

“They were right—Princess Celestia is warm and caring to all her subjects, not just me. But I still wanted her to love me, to maybe someday want to be my mom. I knew she was happiest when I learned something, so I started throwing myself into my magic and my studies. I couldn’t learn fast enough…Everything she showed me, everything my teachers gave me to do, I attacked with everything I had…and for a while, it worked. She spent as much time as she could with me, just us, and she was so proud of me. ‘I knew you could do it, my little sun,’… ‘Excellent execution, little sun!’ …’I hear someone passed their exams today. I had the chefs make your favorite for dinner to celebrate!’ Even when she had to go away for royal duties and diplomatic missions, if she couldn’t take me with her, she made sure we had a way to communicate. I went to all the galas in the palace, all the banquets, all the public events and major holidays. I was at her side for every Summer Sun Celebration and every Hearth’s Warming, her talented and genius protege, who had magic stronger than any unicorn recorded since Starswirl the Bearded and Clover the Clever.”

“I think I cried a little the day I got my cutie mark—” she pointed at the eight rayed sun on her shirt, “—because I thought it meant maybe we were supposed to be family after all. Even the Princess admitted that she’d not seen another mark so close to her own in appearance in centuries…but it didn’t change anything. I was still just her student.”

“And then, the worst possible thing happened. Some obnoxious, cheerfully pink pegasus filly stumbled into Ascension and became an alicorn by accident. Accident!” Sunset clenched her fists. “And what did the Princess do? Adopted her as her niece! That…hurt…more than anything I can really compare it to. Not even the Rainbow and the Elements hurt that much. It gave me incentive though—a solution to my problem. I thought if I could Ascend…”

“That she would adopt you too.”

Sunset wiped her nose again. “…Yeah. Along the way, I turned into a selfish, terrible pony. Nothing mattered but Ascension, the power to change my fate. I didn’t want to be Sunset the Orphan anymore—I wanted to be Sunset Shimmer, Daughter of the Sun like I knew I was supposed to be. We started fighting, and it got worse as time went on. Eventually we had a blow up, except it was in front of the guards and the archivist after she caught me in the restricted section of the library archives. I threw books at her head…demanded she make me a Princess, that I deserved to be her equal if not her better.” Her eyes squinched shut. “…by then, I think I’d forgotten why I wanted Ascension in the first place. I was so angry and hateful and just awful. She was right to dismiss me from her tutelage and kick me out of the palace.”

Luna felt cold inside. She’d had problems with Celestia, with their parents, even with her school as a teen, but her parents had never thrown her out. Her sister had never abandoned her, and she’d always known they loved her. Trying to wrap her head around what Sunset had told her was hard, especially because the mental image she’d formed in the first few minutes of the tale had been of her sister, but as a magical pony of some kind. It just…didn’t add up with what she knew of someone named Celestia, especially one as similar to her sister as Sunset had claimed.

But the evidence said otherwise—Sunset’s reaction to her sister during a panic attack, the description of Sunset’s early life, even the Princess’ pride in Sunset’s educational successes…with the teenager’s clearly emotionally exhausted and worn state, those things were real, and it left her not knowing what to think. She took a sip of coffee, and spat it back in the cup. It was as cold as her innards felt, and she hadn’t even explained things to Tia yet. This was going to break her sister’s heart. Maybe she should be smart…order take out for dinner, get lots of her sister’s favorites, get through this talk first.

She rose and collected her things. School had ended—she herself had let Sunset go home early, though she hadn’t fully wanted to. The girl had insisted, claiming she just wanted to process and de-stress in a place she could relax, and eventually Luna had relented, remembering her own rough days and the need for quiet downtime to recover equilibrium. Sometimes in college, when it had gotten to her the worst, she could remember retreating to her dorm room and hiding in her bed playing video games until her roommate and best friend coaxed her out with ice cream and the promise of take out. It had made her not only give her blessing for the girl to go home, but also to take the next day or two off if she needed it.

Poking her head in her sister’s office, she retrieved the older woman. “Let’s go home, Tia. We’ll order take out, and I’ll tell you what I found out over a stiff drink. We’re both going to need them to get through this.”

“…and that’s the whole story I got from Sunset Shimmer today. She did ask me to apologize to you, and assure you that you haven’t done anything wrong.”

Celestia stared at her sister, before reaching for the bottle of rum and adding a much more generous splash to her mixed drink. Tears were flowing steadily down both their faces, and a pile of used tissues filled an empty takeout box serving as a mini trash can. “I…How could someone do that to a child? How could any version of myself, in any world, not see just how much suffering she was inflicting on a little girl? She couldn’t have been more than…eleven? Twelve? When she first appeared here…”

“That was before I transferred in, Tia, remember? I’d just finished my degree a few years before that, and was still working my way to the admin track.” The dark haired woman thought back, trying to remember the first time her sister had mentioned Sunset Shimmer, but failing that, she furrowed her brows and did the math. “That would have been the year you took over for the kook, wasn’t it?”

“Year after, I think…she enrolled as a seventh grader in the Junior High section.” She shook her head. “She couldn’t have possibly understood any of what was going on with any rationale, not at that age. What was wrong with that woman?!”

“Mare,” Luna corrected, trying to bring a little levity to the conversation that was spiraling out of control, and remind her sister that they were dealing with an alien world with life potentially much different than anything they knew. “…Grown female equines are called mares. Sunset said that her world is filled with talking equines.”

Celestia gave her a hard glare. “…I’m not interested in arguing the semantics of the appropriate terminology to refer to an adult putting unrealistic expectations on the emotional and mental understanding of a child, and of that same adult exhibiting a level of either ignorance or callousness in regards to being the guardian of said child! I don’t care if this other Celestia is a human, a magical horse, or some kind of talking dog!” One fist smashed down on the table for emphasis, a loud thump echoing through the kitchen as the older woman worked herself up into a temper. “How could she raise that girl and not realize that Sunset would attach to her as a mother, especially if she was the sole caregiver from what sounds like infancy onward?!” Celestia knocked back the drink and refilled it with far more rum than soda this time.

“Easy, Tia. We still have work tomorrow. You know you’re a real bear when you have a hangover.” Luna took the bottle away from her and put it on the counter behind her. “As for the question, I don’t know…though I would caution you that we are only hearing Sunset Shimmer’s perspective on the events. It is possible that there is more we don’t know, things that perhaps she was too young to be told or to understand.”

She took a long swallow from her own glass, taking a few breaths as the alcohol burned its way down. “That’s the only way I can reconcile everything myself…by Sunset’s own stories and admission, you remind her very much of her mother-figure, and I know you, Tia. You would never do that to a child, not one you cared for the way this Princess seemed to care for Sunset. You took the same kinds of child psychology courses I did—everything in Sunset’s story makes it sound like her earliest years provided a very secure relationship, and that something changed later on.”

“It doesn’t make me any less angry! How much of this mess could have been avoided if she had just told Sunset she loved her!?” Her sister drained her glass once more and slammed it aggressively on the table with a hard sound; Luna briefly wondered how much more abuse the table or the glass could take before one of them cracked. Her money was quietly on the glass. Celestia’s temper, though rarely seen, burned hot, and she was well and truly wound up by this conversation, far more than Luna had been expecting. “Because at its heart, that seems to be what it’s about. This Princess, for all her immortal wisdom, didn’t know enough to realize that a little girl needed desperately to know she was loved!” Her grip had begun tightening on her glass as she ranted, knuckles going white as she applied more and more pressure to it.

Luna reached across the table to grip her sister’s wrist. “Tia. Stop. You’re going to break the glass and hurt yourself. I know you’re angry. I was angry and upset too. But a trip to the ER at eight at night isn’t going to help anyone.” She let a bit of a smirk play across her lips. “Though, I have to admit one thing. If she was raised by another version of you, I can see where she gets some of her traits. Like her temper.”

Her sister pulled back sharply, chair scraping against the linoleum. “…Not funny, Luna,” she bit out tersely, surprising the younger woman. She moved towards the sink. “How could my counterpart not see it? Or did she just not care!?”

Thinking over some of what Sunset had said, and mindful of the volatility of her sister’s fury in that moment, Luna answered very carefully. “…I think she cared…I’m even willing to go so far as to say that this Princess Celestia loved Sunset. I can think of no other reason she would give her a diminutive nickname like parents so often ascribe to their children. Especially not one that seems like a very telling and personal endearment for what is essentially a Sun Goddess: ‘little sun’ seems a bit on the nose.”

Glass shattered into a million fragments across the floor, with Celestia frozen and rigid half a step from the sink. The younger sister immediately bolted out of her chair. “Tia?” she asked worriedly. “…Tia what’s wrong?”

Fresh tears filled her sister’s eyes as she half turned towards Luna. “…where did you hear that?” she asked, her voice low and thick with pain.

“…I…In Sunset’s recount, she mentioned the Princess’ pride in her accomplishments, and quoted several examples at me. It…cropped up there.” Sunset’s situation was half forgotten amidst concern for her sister. Celestia never responded this way to anything, not that Luna had ever witnessed, and it was starting to scare her. “…It seemed like a personal nickname from the way Sunset used it. Why?”

Celestia shook her head sharply, unable to respond for a few minutes as she shook in place, trying to staunch the tears that had started up again. Luna took the time to clean up the shards of shattered glass, giving the elder sibling the chance to regain some of her composure. As she was throwing away the mess and returning the broom to its home, her sister took one long shuddering breath. “…I’m sorry, Lulu…I lost my head…and you’re right…a name like that wasn’t…there’s no way it was used without affection and love behind it…” She rubbed her face, and Luna realized that her sister was avoiding looking at her. “…there has to be more to the story…”

“Sister?” she tried, reaching for a pale arm.

Celestia flinched away. “…I don’t want to talk about it right now, Luna. Please. Just let it go. Let me have this.”

Her hand dropped away and her mind buzzed with questions, but she backed off from prying, even as her mind made one more notation for the validity of Sunset’s story—in that moment, her sister sounded as broken and hurt as Sunset had in her office, their voices and tones a mirror to one another. Celestia had put up with a lot from her over the years, and had always respected when Luna didn’t want to share, and it was for that reason that she acquiesced to her sister’s plea, redirecting the subject at hand slightly.

“I suppose the question is: where do we go from here? We can’t rescind her punishment, and I don’t think we should. She seems to be benefiting from the structure and consequences of her actions and choices. She was a model student in ISS, she’s been extremely polite to me, and she hasn’t tried to shirk her punishments in the slightest. Other than today’s incident and a few times I’ve seen her brooding, she’s already come a considerable distance from the bully and troublemaker of the last few years. I even had a very positive conversation with her during her last day in ISS—she really does want to do better, and she’s trying to make a life in this world, since she seems to believe Princess Twilight has exiled her here for good.”

Celestia rubbed her temples. “…I don’t know, Luna. Any suggestion I might have, I find myself questioning now that I know her history. The last thing I suspect she needs is another Celestia making a mess of things.” She sounded tired, defeated, hurt, and ashamed, all at once. “…Part of me feels like I should remain strictly professional with her, establish firm boundaries and distance, but I’m not sure if that might not accidentally make things worse.”

Luna sat for a minute or two in silence, thinking. At last, she said, “…Be you, Tia. Don’t think about it, don’t second guess yourself, don’t try to be too familiar or too distant. Just be you, and respond how you normally would. Sunset made it clear she knows that Principal Celestia and Princess Celestia are two different people, and I believe her…particularly with how hard she stressed to tell you that she wasn’t upset with you or blaming you in any way for what happened. I think you just need to be aware that sometimes, she may respond oddly to you not because of you, but because of the memories you accidentally evoke.”

She smiled at Celestia. “It’ll be alright, Tia. Sunset’s stronger than I think even she realizes. She’ll get through this, and we’ll be there to help her when she needs it.” A smirk spread across her face, a desperate attempt to make her sister feel at least a little better sparking her next words. “After all, you survived my adolescence and subsequent delinquency—between the two of us, I’m sure we can find a way to manage one traumatized refugee unicorn girl from a magical alternate universe where they utterly suck at childrearing.”

Luna wasn’t quite expecting her sister to burst into tears as well as laughter, but it was so much better than the pained voice from before that she wasn’t going to question it.

...A great deal of my inspiration on the relationship between Celestia and Sunset was taken from "The Fall of Sunset Shimmer" comic--specifically from dissecting it, panel by panel, and comparing it to what we see of Sun-butt interacting with pony Twilight throughout FiM. There's a lot of little things about what happens there that...seems a little out of place or even ...uncomfortably personal...if you consider their relationship Teacher and Student, but that completely falls into sense if you change them to Mother and Daughter (specifically Mother and older-teenage daughter, since Sunset seems...close to adulthood in the comic but still young enough to be taking exams at the school.) It even makes Sunset's reaction, flight, and later attempts to steal the crown and "conquer Equestria" make more logical sense for a character that is supposed to be Twilight Sparkle's intellectual and magical equal.

It also makes a lot more sense when you consider that Sunset and Celestia have some very similar traits. (Watch the episode where Daybreaker makes her appearance, and compare it to Sunset as a demon. The similarities are...striking.) And Sunset's later behavior in the Equestria Girls movies/specials continues to show parallels between her and Celestia. I could also go on about symbolism and and elemental properties, and such like that, but I've already talked the ears off my spouse and beta-reader about the Sunset-Celestia relationship.

I also make use of one Princess Mi Amore Cadenza and the loose idea of her backstory, to add in some interesting pressure because she does appear in the Sunset backstory comic (looking like we see her in the flashbacks in the show from Twilight, as a gangly teenager who isnt fully grown with a tiny blank flanked Twilight sparkle, where Sunset in the same panel seems to be much more physically grown into her body, implying she was older than Cadence and Shining.) I do go with the time distortion between the two worlds, but I've actually come up with exact numbers, and woven it into the worldbuilding backstory as to why it happens and how, and what changes as time goes on.

As for Human Celestia's behavior.... Well. In the words of Xelos Metallium: "Sore wa himitsu desu."

...I kid. You'll learn more about what our dear principal is hiding as the story goes. >:}