So this is the product of me thinking about this lyric from a Halsey song and the fics Once More, With Feeling and Out of Hand at the same time, and then me finding it in my drafts months later.
It's the Eternal Night. Jim's body lays behind Claire, struck down by a blow that was meant for her and her friends. She doesn't know if he's alive or dead, but Morgana has just killed Angor Rot. The only viable option feels like screaming "Die, witch!" as Claire tackles her into a portal into the Shadow Realm
In another universe, Claire fights her way out and the Shadow Staff is destroyed.
In this universe, Claire wakes up.
It's several months in the past.
Specifically, it's the morning that Jim would have become the Trollhunter; the morning that Kanjigaar died.
Claire can fix this.
She sneaks out of her house, early, saying that she wanted to meet with a teacher before school on a Post-It Note. Perfect Claire meets with her teachers so that her A's become A+'s in the grade book.
Perfect Claire hasn't ever had her brother and body ripped away from her.
She's not going to let it happen again. She's going to use the knowledge of the tenth grade that already happened for her and make sure that everything goes right. She's going to train to become stronger and smarter. She's going to have Straight A's and make sure that Enrique stays on Earth and make sure that Jim doesn't get killed by Morgana.
Claire shows up at the canals, thankful for all the track and field she did. She can run.
She could throw a javelin. She won't need to throw a javelin because she won't use her Shadow Staff, won't need it. She'll miss it. She won't miss the feeling of her hands and face cracking, of her soul being ripped and torn and poisoned.
"Claire Nuñez," the amulet says after a moment's hesitation. Claire smiles. Merlin won't be able to take Jim from her. She loves him, and will admit that his troll form is hot, but she saw how hurt he was by it. Besides, Jim deserves a life outside of being a soldier.
Claire picks up the amulet.
"Well, you didn't think that one through, did you?"
Claire wants to drop the amulet but she can't.
"You pushed me through the portal," Morgana says. "My hand is in the amulet."
Now and for all of time extends to the past, too.
I'm tempted to write a sequel titled "I'm Such a Fool for Sacrifice". Let's just say it's going to deal with Angor Rot and will be dark.