Was this an allegory for teenagers losing their innocence and becoming independent from their parents?
It was about a pervert discovering she was a pervert by going to a school full of perverts and fighting the head-pervert with the help of some retarded girl and her retarded family.
It was part of confidence and being comfortable in your skin. Ragyou was trying to make Satsuki stronger through sexual therapy.
Except it was obviously a perversion of theae concepts by Ragyou who had lost herself along the way, showing she is the villain.
It was actually more about severing the "sealed fate" or red strings. Matou is someone who's designated to make the change that happened in the last episode.
It's basically a new spin on magical girl transformations, shounen and female MC. Not too far removed from shows that come in bulk every season but unique regardless.
"growing out of school uniforms" (this was real easy to catch and literally spilled in the OVA), "embarrassment of inappropriateness", maybe some more that fly over my head. Can be linked to strict school rules in regards to uniforms (compare: some European or American countries), purity culture. It's hinted everywhere, look at junketsu for instance.