Sayara Yamanobe is pretty screwed up in the head. She pierced poor Rin in every place imaginable, cut open test subjects while they're still alive and using their DNA to make clones, the failed test subjects she kept locked up instead of killing them and ending their misery and when Rin escaped open the doors for them to get Rin (kind of like a Resident Evil thing), and then tested on Rin later on without any numbing meds and letting her feel the pain as they cut out her organs. (Rin's immortal if you're wondering how she could still be alive after all of that).
Even though I'll admit I do love her (in a way..especially when she acts adorable!)..but O find that Rena-chan from Higurashi would fit this label..why?..I mean just the way she acts even at times can be extremely scary..I mean she can either be really cute یا really scary..but I find that her actions actually دکھائیں it the most.