Another problem I have is that the current antagonists are in fact a bunch of writing sins in one pot.
They can strike pretty much out of nowhere and then teleport away, which is just a completely cheap way on them getting the drop on the main characters.
And what the "Oh, her turning into a youma was for the theme" overlooks is that she very much was fridged.
Shortly after her introduction, the new antagonists appeared out of nowhere, forced her transformation with a hithertho unintroduced concept of the instant youmafication(Which honestly works against the theme of the ninyou having to keep that part of themselves in check), then teleported away with no consequences to them at all.
Honestly, I gotta say it, the story is competently written, but badly so. The author isn't an amateur with his first draft, but knows how to write, it's more that he has chosen established but terrible tropes to create his antagonists. A thing I also saw and loathed in "Jungle Juice" which had the exact same problems with their main antagonist group.