Time for the Scooby Doo villain reveal...
The rebels (him at least) don't come across as wanting to really change the system so much as change who is on top and on the bottom.
I read this some a while ago and I don't remember if this the kind of cultivation story where the MC has a murder boner or if that's a different one. Fights Break Sphere, I think.
Was he really a soldier in an army? He should at least know the basics of the different kinds of weapons. It turns out that what was meant by "Demon King's Aide" is "Demon King's Bed Warmer."
There was some Medieval era isekai where the protagonist introduced pottery and it was such a great invention that nobody had ever heard of before. Apparently, they were cupping their hands to transport water from place to place. I stopped reading after that.
A good reason for not developing...
"Everybody only wants to be Mutsumi's friend." Oh, I don't know. Maybe if you stopped acting like a psycho hose beast rapist and stop trying to get everybody killed, they might like you a bit more.