Ah, four new characters. Each of them look like interesting additions.

Zarah, waiting with curiosity what you might pick as your character's abilities.

CMOTDibbler, are you planning on giving history to your character?

Kasanip, your character is fine, but there were few terms I couldn't comprehend. What does 作中 mean, and what is Enkyorisoukikeikai?

Horngeek, I was going to say something about how it makes no sense for a Substitute to know Kidou spells without going to academy, but your explanation of her reverse-engineering them from spells she has seen is plausible. (I applaud you for accounting for the fact that she would be oblivious to exact numbering and classification of her spells.)

However, there's a bigger problem here: namely, why was Hinata made a substitute? Four years ago there was still dearth of Hollows, since for 50 years before the story Hollows of Hueco Mundo were hiding. This disallows random Hollow attacks, so only a recently-born Hollow could've attacked Hinata, meaning it must've been a person close to her.

This is something you and Kerfuffle need to spend some time thinking. How and why could a new Hollow have made an experienced Shinigami like Ariana do something as drastic as give a 12-year-old girl powers and then leave her behind just like that?

This goes doubly if Hinata had Fullbring already. Why was that not enough to defend herself?

I can imagine at least one sequence of events that would explain it, possibly without involving Hollows at all: another person forcing Ariana to Substitute Hinata. But again, why is a big guestion. I can think of one person who would do that, but he wouldn't have been able to do it four years ago.