Mizuki's story absolutely screams transfem and it makes the most sense to me, but it's not wrong to consider them non-binary. It's not confirmed either way and we don't get what they're preferred pronouns are cause that doesn't really exist in Japanese.
Assuming their pronouns are "she/her" and that they have to be transfem is just as presumptuous as saying they're 100% non-binary, both interpretations are consistent with the story and acceptable.

Poor Kanako watching her daughter/shrine maiden get rizzed up

Mizuki is happy presenting as a women the whole series and is deeply afraid of being seen as anything else. I feel like being a cross dresser or even non-binary is a bit of a stretch because they very obviously just prefer identifying as the one gender they're presenting as. (though, you can definitely consider them non-binary if you want.)
It really doesn't make sense to use "he" pronouns when Mizuki obviously wants everyone to consider them female or at least non-binary. I mean, their greatest fear is being outed as born male.

It's parodying a (particularly fantastic) scene in The Chainsaw Man Reze Movie.

Goated series and chapter

Not sure if the author was processing something or just wanted to write a fairly bad main protagonist of this short story but her cognition of the world is totally backwards. Azu is the fake one and the people trying to get their revenge on her were fairly forthright and honest about it.

Everyone here kinda sucks and not even in an endearing or hot way, just kinda annoying

Rena is really judgy and seems very cynical about her classmates and probably people in general. Azu is 100% trash, but predictably so and is complete upfront about it to Rena. Rena seems to prefer someone she can trust to be bad over people who try and save face and lie to her for whatever reason. I think this makes logical sense in her mind and that's enough for me to accept it, it doesn't need to be something we necessarily agree with.

This is just me, but I don't think the characters are really getting away with being this way, with Azu getting punched and Rena being a loner. For me, as long as the author isn't rewarding them for their behavior, it's kinda fun to watch toxic people find eachother and be toxic towards one another. The characters felt consistent and they do feel like a good (bad? Probably.) match for one another.

Plus they're highschoolers and they aren't sociopaths or actively abusing anyone, they aren't forever irredeemable.

@SchroCatDinger why are you so desperate for attention? The same comment under like several posts makes me thing you aren't reading comments properly.