Though she's a snake, Miia had never shown the classic long tongue we'd come to expect from her race. That is, until chapter six. It is REALLY jarring, especially since it's A. a HUMAN tongue, and B. evident that at this point, Miia is not exactly...herself.
Chapter 11 can come across as this initially until it's revealed that the women aren't actually as helpless as they first appear.
Chapter 13 has the girls trying to help a sick Kimihito through Suu, as she is the only one immune to cross-contamination. Their attempts are pretty much universally funny (Miia's cooking makes a triumphant return), but then they get to Papi's attempt. It manifests as Suu bearing down on Kimihito with her arms morphing into wings, parroting the argument that the rest of the girls had with Papi in a strained distorted voice, all the while having light shining out of her eyes and mouth a la NicoleBrennan◊. JESUS, Suu. This is in-universe Nightmare Fuel: Kimihito is terrified!
Rachnera is quite the intimidating sight, particularly compared to the other girls. Picture a woman with the lower body of a spider the size of a king-size bed, six eyes, and razor sharp claws, whose first full appearance is her hanging from the ceiling, glaring down at the reader in a pose suggesting she's ready to pounce. And to top it all off, the very first thing she does in her introductory chapter is mummify the villain of that chapter in silk, for reasons that are likely best left to the imagination. While it's apparent by the end of the chapter that looks can be deceiving, and she's not quite as terrifying overall as she first appears, God help you if you piss her off.
Centorea was damn nearraped by a gang (led by the one Jerkass from previous chapters) in Chapter 16. For one, it is certainly not played for laughs, and considering the rules of the program (extraspecies cannot harm humans), she was rendered totally hopeless when Kimihito is held back. Luckily, Rachnera intervenes and scares the shit out of them, but damn the manga got dark for a second.
Rachnera's method of scaring said gang also counts, providing a delightful little Nightmare Face just pictured above.
Although they probably wouldn't mean to harm Kimihito due to the fact that the incident occurs during The Full Moon, the fact that they (Miia, Cerea and Papi) lose control over their strength would mean a rather fatal intercourse.
As of Chapter 18, Kimihito's life is in danger. Someone has sent him a death threat if he marries any of the girls.
Miia almost gets raped in Chapter 19. She's out in the middle of a lake, in a small boat with her captor, and there is barely anyone around.
Chapter 20 reveals that there are traffickers that kidnap monster girls. The girls in this particular chapter are children.
They were naked, too. Make of that what you will.
Chapter 22. The Dullahan. We haven't even seen her face yet and already she's terrifying. Her first true appearance was her standing across the street, staring at Kimihito hidden in shadow. A truck passes, and she's GONE. Suddenly she's behind him, INCHES from him. She has a wickedscythe in one hand...and her head in the other. Then the scythe is around his neck as he's realizing what's happening...and the chapter ends. Chilling.
Chapter 23, Lala casually mentions that there is an entire organization hunting her. She claims to essentially be Death itself, there is something hunting her, and it's enough to make her feel rushed enough to present herself to the living.