I read this manga a while ago and I can't remember the title. It's about a girl who's a clone of this demon queen long long time ago. She didn't know it, and she lost all of her memories, she thinks she's this normal girl who moved. And her family is brainwashed in thinking that she's their daughter, she ate their daughter and all the memories transferred to her. I think her demon queen name is Souryo. She then finds out everything from the byakko, she falls in love with the guy, her "parents" turn into demons. Then, she doesn't want to be the souryo, but then she meets her sister who does want to be the souryo but she's evil or something. Then the guy's family want to kill her because she's dangerous or something.
It's a shoujo fantasy manga.

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♪MONSTARR~ will eat all your cookies and steal your bishies~♪ Φ_Φ

It's Ao no Fuuin.

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*poof* "SHOUJOMAN IS HERE!"
~Just Lynz, drop the -ajw~

Ah~ How could I not remember that! Haha, thank you!

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♪MONSTARR~ will eat all your cookies and steal your bishies~♪ Φ_Φ