In the genre section of this manga, it says Mature. I feel like it's more adult. Am I wrong?

It´s more the gore and body horror that stands out. The graphic sex is frequent enough and over the top, so feel to throw Adult on too but I would absolutely keep the Mature as it´s impossible to describe the manga without mentioning the violence.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb

Ok sure.

Well it won’t let me add adult so I guess we’ll leave it at mature lol.

You can petition the admins via Request Change to add it if you give a compelling enough reason. An argument can be made, especially if you add a visual sample. This is primarily a hyper-violent body horror comic but it misuses rape like crazy and the gratitude sex scenes could have been published as porn with no one batting an eye. I don´t mind this having both, some manga are like that. Again, it´s up to the admins.

The genre box is in lockdown as I myself wrote for it to be locked due to someone drowning it with (conflicting) genres. This may be a genre and tonal clusterfuck but (re-)adding over a dozen genres with little regard to logic sets an abysmal example. That´s why the toys had to be taken away.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb