We have the Talented students, aka those who have special powers. And Nana, a normal human, in other words, a Talentless.
Nana was the first female main character I knew, who can also be classified as the 'bad guy.' And that I think, made her set apart from other MCs. (If I'm wrong, and you know any character who's similar to her, do notify me in the comments below.)
As someone who's playing a dual personality, she really did play her role well. Thus, making her a good killer.
Amongst the rest of the class, I found Nanao Nakajima to be the most powerful. I know Kyouya can recover fast, but if he didn't know Nanao's talent, and he touched him, his ability will be nullified. Nanao, can then just kill him with a mere knife.
Regarding those two, I can't help but be reminded of two Marvel characters who have the same skills as them:
Kyouya's ability was similar to Wolverine's fast healing/recovery. And Nanao's nullify power was akin to Leech, aka Jimmy.
Michiru Inukai on the other hand was the hero of the show. No, she didn't do any heroic stuff like fighting and such. But, she did make Nana question everything, including the death of her parents, and the Potential Kill Count information given to her.
It was thanks to her, Nana started to question things, and will now seek the truth.