Sun's house, many moons ago
Sun's face was blank. It was blank since she woke up, and it was still blank even hours later. Her house felt empty, and she knew why. She couldn't read, write, draw, or really do anything. It felt like she'd lost a pet, but she only thought of her like that because it helped make her feel less like she'd lost her best friend.
"Sun?" Twilight knocked gently on Sun's door. She answered the door, and was met with Twilight, who telekinetically held some kind of gift, clearly for Sun. "Hey... How are you doing? Everything okay? Any symptoms of depression?"
"Oh, I'm far from depressed, Twilight." Sun laughed, showing the first sign of any emotion she'd shown since yesterday. "I'm just... y'know, taking a day to relax after all that's happened. There was this whole part of it where I talked to Avalonia before she sacrificed herself that I didn't tell you about." Her complete honesty was actually a little weird, since made her look like she wasn't affected at all. Maybe that was just what she wanted Twilight to think.
"Do you maybe want to tell me about it over some cupcakes I brought for you?" Twilight offered with a smile.
"That would be nice." Sun sighed.
Twilight came in the house, and the two talked for a long time, but mostly about things other than what happened yesterday. And when Sun did bring up the day's events, she was rather factual with it, not bothering to express her own opinions, although Twilight could gather how she was feeling from subtle pauses and picking up on certain tones she used while describing how something happened. Twilight was beginning to wonder if Sun was even hiding any feelings from her.
The unicorn's mind always felt... clouded. Even she had a hard time figuring out how she truly felt about something. She always chalked it up to her not being the smartest pony (that is to say, she was assuming she was too dumb to feel profound emotions like grief), but it was becoming more and more obvious that she simply ignored thinking about bad things, probably as not to have her maturity crumble because of its neglected, fragile foundation. Perhaps it was because she wanted to get away from the supposedly-immature pony she believed herself to be before.
She wanted to desperately hang onto the idea of a simple life - one where she didn't have to worry about sadness or death, and could just enjoy the mundanity she was promised when she moved to Ponyville. So, she simply didn't worry about those negative things. She just moved on from them before they could affect her. She just took everything day by day.
Twilight didn't exactly see an issue with her philosophy, but it probably wasn't the best attitude to have to ignore all your problems. So, she thought of an idea. "Sun, I think I know someone who can help you feel better."
Later
"Sun, meet Starlight Glimmer." Twilight gestured towards a unicorn at the door. Her coat was a pastel pinkish-lavender, and a moderate purple mane with a light greyish aquamarine stripe. Her kind, oval-shaped eyes gave off an aura that was desperate to gain Sun's trust. "You can tell her all your worries, because she's quite a good therapist."
"Hello, Sun." Starlight greeted with a meek grin. Sun was going to greet her back, but she was suddenly taken aback by her voice, because it sounded familiar.
"Wait, have we met before?" Sun asked. Starlight was also surprised by hearing Sun's voice, as it seemed to ring a bell.
"Have we?" Starlight wondered. "I've obviously heard a lot about you from Twilight, but I feel like I've heard your voice before." Twilight groaned. Sun getting another lead on finding out her past was a perfect excuse to avoid talking about her problems. "I can't put my hoof on it, but I could swear I know you..."
They both felt so close to finding the answer... but the fog clouding both their minds was too thick to see through. "Oh, well. I'm sure one of us will remember eventually. So, why don't we get started?" Starlight walked through the doorway, and sat on Sun's couch along with her. Twilight decided she'd leave them to talk, and went back home.
"Twilight's been filling me in on some of what's been happening, but the way she's talking about you is telling me that there's a lot more going on. You wanna maybe tell me about it?" Starlight asked, gently persuading Sun to talk about things from her perspective.
"Oh, well..." Sun began. "since the moment I've arrived in Ponyville, I've found out that I lost all my memories, I've absorbed an evil spirit into my body that haunted my dreams every night for a while, I've been attacked twice by a goth psychopath who thinks of me as her mortal enemy, I've almost died several times, I've had to learn to forgive that evil spirit I absorbed after me and Luna had to battle it throughout a bunch of different ponies' dreams, I've battled another universe's version of myself, I've done unspeakable things I don't even wanna talk about, I've had my heart broken and then had to fight off a Changeling invasion by myself before going berserk and attacking a princess, and then, I was being attacked by this punk pony when suddenly a Nightmare Moon-esque version of myself from the future appeared and told me that the evil spirit I absorbed, whom I also became best friends with, is basically gradually killing me without knowing it and is going to bring back an ancient evil that would destroy Equestria, and then I had to go on this whole journey that ended with me killing my best friend to stop said ancient evil. So, I've been a little busy the past few weeks, as you can tell."
Starlight took a deep breath, and exhaled. "OKAY, that was... a lot to take in. What was that about... well, everything you just said? That must've been a lot to deal with in just a few months of living here-"
"I've only lived here for three weeks."
"Sweet horse-angels above!" Starlight exclaimed in horror. "Are you okay?!" Thoughts began to pile in her mind as to just what Sun could be feeling, but even she had no idea - she could only begin to imagine what was going through this poor little unicorn's mind. In fact, Starlight was only further confused when she noticed how Sun talked about them like they were just funny things that happened to her, and her reply was the cherry on top of her cake of dismissiveness.
"I'm fine."
Just what was going on inside this pony's head? It was becoming impossible to tell if she was completely lying, or being completely truthful. It was jarring to Starlight how little Sun cared about everything that had happened to her. All that Starlight knew about her before coming to talk with her was that she'd just lost someone close to her, and that seemed to be the only thing in the list of horrible experiences that Sun actually cared about.
"You know you can be honest with me, right?" Starlight reminded. "Is there anything you maybe want to get off your chest about your friend? I'm all ears, and you can be 100% honest. I won't judge."
"Well, I do have some things that bug me about Avalonia dying." Sun said, namedropping her late friend for Starlight as she began to finally open up. "It feels like just after we got friendly, I suddenly find out she's going to kill me and cause all this evil stuff to happen. It's like we became best friends right before I had to say goodbye to her. This kinda thing's happened before - I was becoming good friends with Fluttershy, but then I went and ruined everything by telling her I started to get feelings for her. I haven't really talked to her since. I feel like the universe doesn't like when I'm happy."
"I know it can feel like that," Starlight replied, putting her hoof on Sun's shoulder. "but no one's out to get you... At least, not in this whole cosmic fate sense you mean. I know life seems like it's nothing but darkness ahead, but trust me... it gets better. You just need to make an effort. You have to get out there and make it better."
Sun was touched by her words, as they kind of reminded her of what Avalonia once told her. It hurt the yellow unicorn's heart a little to remember Avalonia again, but she quickly forgot about that brief pain as she took in Starlight's words.
"Thanks. I'm gonna take your advice. I'm going to go back out into the world, and probably get a job or something!" Sun proclaimed with her newfound sense of hope. "And hopefully, I won't be jumped by any new ponies today... or that guy who owns my life."
"Yeah, that's the spirit! ...Wait, what was that last thing?"
"N-nothing!"