She's a billionaire

She looks simple as you look at her. She wears thigh-length skirts with tight pants or long socks underneath. She looks weak and poor because of her poor sense of fashion but she talks cool and calm. She does not usually smile and had no time making friends. She was focused on avenging. She is silent but is really good in observing people. She is an assistant of a superstar before.  A strong g**g of the underground society wants to make her their friend. She has many shadows and allies that protects her. She met a Mafia Prince who's mission is to capture her. She met a royalty's son who's going to help her. She faced unexpected challenges and new people that will be part of her life, unexpected downfall, unexpected war, and unexpected betrayal.  Why?  It is because she is the KEY to get that large amount of money and the city that they were seeking for. Who really she is? Because she's a billionaire?