Forgotten Title Noble lady got executed and turned into a ghost to find out who killed her

Main female (not ghost) attended a castle party and meet the ghost, ghost girl impressed that this chick and see her. They had deal where ghost girl will help her with noble lady society stuff in return main female will help her find out who orchestrated the stuff that caused her to get executed.

MF about to attend her debut party, at the party she discovered that her fiancé is cheating (kissing) the bitch (first villain) . The bitch ordered another girl to accuse the MF of stealing her tiara and exposed her in the middle of the ball. Ghost girl then possess MF and dealt with the situation.

Main female appearance is, according to memory, pure innocence short hair short stature.
Ghost appearance, wavy black hair in a red and black dress with a rose hair ornament.

This is a manga, according to my brother, but I don’t believe him.
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Holy Grail of Eris.

NU Link

Mangadex Link

 

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Dang. Just when I find a title I know. I wasn't quick enough..