Mabel sat by herself on her bed, holding a snowglobe. Just looking at it made her uncomfortable, but she did it anyway. Not that there was anything wrong with the snowglobe itself, though. It was a birthday present from Grunkle Stan, and it was fairly well-made, better than the tacky ones the Mystery Shack sold. There was a model of Gravity Falls in it, pretty detailed and well-painted.
What made her uncomfortable about looking at it is that whenever she did, it reminded her of the mistake. The really big mistake. The biggest mistake anybody's ever made. The big dumb awful mistake that she made, and somebody else had to fix.
She caused the apocalypse. As far as she knew, nobody else on Earth could say the same. So many people suffered because of her. The entire world nearly ended because of her. Dipper had to survive all alone for three days in a monster-riddled wasteland because of what she did. Grunkle Ford was turned to gold and tortured by the demon that she was responsible for letting into this world. Grunkle Stan gave up his memories and almost lost them forever to fix a mistake she made. Her friends were all either turned to stone or forced to hide from monsters all because she was so selfish and so stupid.
And what did she get for doing something so awful? She got to stay in a magical bubble where all her desires came to life. She lived in a paradise while everybody else suffered because of her mistake. She had it easier than everybody else in the entire town, and she didn't deserve it at all.
Mabel started turning the snowglobe around to look at it from different angles. She had hoped nobody noticed how uneasy she looked upon receiving the snowglobe on her and Dipper's birthday. It's not like Grunkle Stan could have known how uncomfortable it would make her, he didn't know what she had done. Nobody did. She really should tell somebody, but she couldn't. Especially not Dipper.
Not because he would hate her, or never forgive her, or anything like that, but the exact opposite. He wouldn't blame her for a second. He'd tell her that it wasn't her fault at all. He'd reassure her and say nice things about her, and he might even say it was actually all his fault.
And if, after everything that happened, after she caused the apocalypse, after she caused him to have to survive by himself for three days in a wasteland that was her fault, after she replaced him with Dippy Fresh or whatever he was called, after she refused to help fix the awful mess she made until he gave up his dream for her, if Dipper ended up blaming himself for what happened, she would never be able to forgive herself.
He probably would blame himself over Mabel, because he's such a good brother. Way better a brother than Mabel deserves, that's for sure. The least she could do was not tell him about her guilt, which would just be one more thing for him to feel bad for. Sure, it hurt to have to keep this whole huge secret from everybody, but she deserved to suffer. She deserved so much worse than this, but it's a start. She sighed. Maybe everybody would be better off if she had d-
Her train of thought was suddenly cut off by the door opening, startling her into dropping the snowglobe. She tried to catch it, but it toppled out of her hands. Not being able to bear seeing it break, she turned away and closed her eyes.
Tears welled up in her eyes as she cried "No, no no no, not again!"
After a few seconds, she realized that she hadn't heard a horrible crashing sound. She turned around to see Dipper holding the intact snowglobe. He had caught it just in time. He was such a good brother, he didn't deserve to have such a selfish, rotten, poop-for-brains sister.
Dipper handed her the snowglobe and said "Mom told me to tell you that dinner's ready. Sorry, I didn't mean to startle you like that."
To an outside observer, the tearful smile that Mabel gave would appear far more grateful than the situation called for. "Th-thanks." she said. "You're a... you're a really good brother."
Dipper looked concerned as he said "You're welcome. Uh, is everything alright?"
Mabel realized how odd her reaction to dropping the snowglobe must have appeared.
"Oh! Well, it's just, you know, that it was a present from Grunkle Stan and also it's kinda like a memory of Gravity Falls so that's why I didn't want it to break, you know?" said Mabel.
Dipper didn't seem entirely convinced, but thankfully he seemed to realize that she didn't want to talk about why she was acting like this now, though Mabel wasn't sure she ever wanted to talk about it. He also didn't ask what "not again" was supposed to mean, which was also fortunate.
"Well, alright." said Dipper, still looking concerned. "Uh, like I said, Mom says dinner's ready."
"Yeah, I'll just be a minute." said Mabel.
Dipper nodded and left the room.
Mabel took one last look at the snow globe before gently placing it on the shelf, making sure it was secure.
As long as she was alive, she would keep this snowglobe safe.