Momo Karuizawa

She may still look like a kid, but she actually has a naughty and impish personality. On top of that, she's cruel and atrocious. Her dislike of big girls is shown when Natsu shows her mistrust towards Momo from within their first meeting, which leads to an argument between Natsu and Shoma and despite Momo's true alignment being revealed later on from within the storyline, Momo herself is capable of displaying real genuine feelings via Momo's emotional breakdown after being betrayed by her own boss, Kurow.