For some, Mario Natsume is FREAKING CREEPY. The first thing he said in the series is "SURVIVAL STRATEGY!", he has his own Penguin Hat, shows absolutely NO emotions otherwise, freaks the shit out of the otherwise Hot-Blooded Kanba when they meet without saying a single word, is the center of his sister Masako's "Project M"...
Even worse in episode 16. When he finally gets to talk some more, it's because his grandfather's spirit is using him as a Soul Jar. AAAAUUUUGH.
Episode 14. Yuri drugs and tries to rape Ringo. NO ONE COULD SEE THAT COMING. Even worse is how Yuri is VERY mentally broken at that point and does this while mentally repeating how much she hates herself due to her body issues and loneliness.
And then we have episode 15. First there's Ringo's extremely erratic behavior and words as she calls Shouma while drugged and about to be raped by Yuri, which causes Shouma to freak out. And then we have Yuri's past as the victim of a rather... special, to say at least, type of physical abuse (as well as horrible emotional abuse, and maybe sexual as well) from her terribly creepy father. Who also happens to bear some vague resemblance to Touga's rapist stepfather from the Revolutionary Girl Utena movie. GAH!
Episode 17 and 18 have Tabuki as the freaking Master of this as he goes from kind and slightly off-kilter school teacher to totally unhinged would-be killer who takes Himari hostage and almost gets her and Kanba horribly killed.