Eiko, make certain you are never alone with that girl.
4) Nishimura is a crossdressing male (see ch24). He hasn't really gotten enough focus thus far to determine what his deal is (ie. sexuality/gender identity/etc.) but he seems to be an LGBT ally if Enami's comfortable getting drunk around him.
I just read through chapter 24 again, and there was nothing in there that made me conclude ANYTHING like this. At all.
You missed it, like I did too till it was pointed out - it has not been raised in the story