Not only did this Anime dare to show a female rapist, but a brutal, lesbian rapist. I won't spoil how the protagonist kills her, but that's sure to have caused salt also.
Assuming the commies didn't just cry about the first couple of episodes then move on when it became clear they wouldn't cave.
They probably wouldn't give a shit about Nagatoro bullying Sempai. Gurl Powah, and all that. More than likely if they're bent out of shape over anything it's because Nagatoro is secretly simping for Sempai.
Either that or they've got their knickers in a twist because it's the usual "underage Japanese kids wanting to bone down with each other" plotline, but in disguise.