Okay au where a sibling other than Five gets stuck in the apocalypse (im voting Allison because she's my favorite and also it works the best for her character and the plot, sue me) anyways Five opens up a portal or something and she gets pulled through and ends up alone, with no one to rumor, basically powerless for 45 years
It fucks with her.... so bad.... because all she wants at that point is people to love her, to see her, and suddenly there's no more people!
But unlike Five, she can't get out. There's no hope, nothing. She can't time travel! She can try and try and try to rumor her way out, but she can't just make a fucking portal appear out of thin air! Maaaaybe she can heal herself if she gets in trouble but depending on your hc with her being able to rumor herself she could be totally helpless
Helpess and without Claire! And with no Claire, Allison doesn't realize how awful her powers can be, giving us a hella powerful trigger happy (literally, once she gets picked up by the commission) superpowered badass running around town
Like honestly, could you imagine how cool some of her fight scenes would be? Just oh my god... and unlike Five, she wouldn't be in the apocalypse of her own fault and probably blame her family (especially the TIME TRAVELLING brother who put her there) for not finding and getting her out in all those years... instead of stopping the apocalypse for her family she'd be doing it in spite of them... like she'd probably have some tenous connections with people like Luther, or Klaus, or maybe(???) Vanya if her book helped her realize anything emotionally speaking but still, I would NOT like to see the result if she ended up with a gun to Vanya's head again, nosiree
Just... thinking about Assasin!Allison using her powers like nobody's business and stopping the apocalypse, not for anyone else, but because she wants to live the life that was stolen from her years ago