Boku no Kirai na Shitsuji!

Due to the fact that Kotori's father wanted a male heir, as the older sister she tells him that she will become the male heir instead! So far her secret has been hidden until a strange new handsome butler shows up and turns her already crazy life upside down. Now, people are starting to take notice of her.
And Problems keep on coming! Her secret gets exposed by a male classmate and he is forced to stay with her and keep her secret safe. And she's got a crazy girl stalking her who thinks that she is a boy and wants to become her lover!
(Source: LuffyNoTomo Translations)