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(MANGA SPOILERS FOR THE NERDS WHO HAVEN'T FINISHED READING JJK AND ARE WAITING FOR THE ANIME ADAPTATION, GET YOUR INTRIGUED LITTLE EYES AWAY FROM THIS TEXT PLEASE)
Y'know, I was thinking about this earlier today and didn't write about it before cuz it sounded kinda silly but we all know I love me some silliness so I'm gonna talk about it now. So. Domain expansions. Wouldn't Spices be able to have one? While yes, the main point of a DE is to basically try and guarantee the kill on the opponent with the sure hit effect of the domain, anyone with enough training and ability should be able to pull it off since (to my understanding of how they work) domain expansions are the sorcerer's inner domain brought to the "real world/material plane" (since we've seen characters like Megumi and later on Yuji do their domains with zero prior training at attempting to open it) and while Spices' wouldn't be as strong due to their lack of a technique (as far as we know since I know you're plotting something Author, I am not crazy, it's gonna be the most obvious and stupidest technique ever I just fucking know it) its still a domain at the end of the day. Provided it wouldn't beat actual domains like Gojo's, Sukuna's or Yuta's to name a few, it's still basically a prison which is almost impenetrable from the inside unless the opp has their own domain. Anyways thank you for coming to my TED talk, I'll be sitting in the shadows if someone requires my presence, have a nice day, afternoon or evening wherever you are. Peace.