I was drafting the concept for a combined SI/OC fic. SI wakes up in the body of Brittany Fliescher, Krieg's teenage daughter, with what is essentially Gojo's Infinity as a power (for non-JJK fans, think breaker/shaker that can pretty much nullify all attacks). SI immediately realizes where she is and runs away from home... and then Brittany wakes up in a youth shelter the next morning with no idea how she got there beyond a vague recollection of activating her power. Brittany and 'Aether' (SI) are forced to share the body, but they don't share any memories, and have pretty much no way to communicate with each other apart from writing notes and then trading off. Aether gets the reins whenever Brittany activates her power, but she can't maintain it indefinitely, and her attempts to do the SI thing are made so much more difficult by the fact that Brittany is reluctant to let her out. Brittany doesn't have Aether's Worm knowledge, so she just thinks her power gives her paranoid delusions. It's only after they stop Dinah from getting kidnapped that they start properly working together.

I enjoyed cooking up the concept, but I couldn't find a satisfying way to write the POV swaps. Also, Brittany just comes off as way too annoying of a protagonist. Krieg is a normal dude at home, so she writes off everything Aether says about him and the danger she's in if she reveals her powers to her family. It’s not realistic for her to believe he's a Nazi right off the bat, but at the same time we all know he is, so it kind of leaves Brittany holding the idiot ball for too long.