Kujakuiro no Canary

As Akiko's mother lies dying she confesses that she has a twin sister who was taken in by a wealthy man. Unlike Akiko who grew up impoverished and shunned, this sister lives a life full of decadence and adoration. Like the Canary who killed the Peacock to be the king of birds, Akiko resolves to acquire her lost sister's life at any cost.

Note: contains the one-shot Pollyanna no Kishi (ポリアンナの騎士):

As a little boy, he saved her life before she was even born. And as she goes through life, Pollyanna will meet her 'knight' again and again.