Naoko Kirino

Naoko is a cheerful, childish and intelligent girl, she has a passion for Halloween and was shown to be very excited when she was crowned the "The Pumpkin Queen", she also has a strong personality and isn't willing to give in to anyone, she'll do what it takes to have her way.
Because of the trauma, Naoko has become a psychopathic, sadistic and ruthless girl, killing mercilessly her bullies and innocent people.
She also mispronounces other people's names on purpose (e.g Chaki, Kachuya, Nyaruto, etc).

(Source: Pumpkin Night Wiki)