Oujisama to Haiiro no Hibi

Atsuko's father is a drunk, and she's shunned by her classmates as "the poor kid." Walking the streets in a dark fog of despair, Atsuko cons perverts out of their money to survive. Then, one day, she meets Itaru, the heir to a wealthy family, who happens to look exactly like her. Itaru hatches a plan: Atsuko will live his tedious public life for him, and she will get a taste of the luxuries enjoyed by the 1%. Everybody's (finally) happy. Right?

(Source: Kodansha Comics USA)