Changing their Fate (Book of Circus)

Ciel Phantomhive was not the only survivor of the Phantomhive family, his elder sister survived as well.
Y/N Phantomhive is the eldest child of Vincent and Rachel Phantomhive and older sister to Ciel.
When she learned about the contract her younger brother made with a demon, she was sad and angry.
Angry, that her brother sold his soul to a demon and that his life will end sooner than it was supposed to and Sad, that her brother made this choice because of the pain he endured, the pain she failed to protect him from.
Many things have happened since that night, including being named as The Queen's Vulture, the siblings came up with 4 rules.
1. Follow the Queen's orders
2. Complete the case, every single detail of it
3. Never lie to the Queen
4. Don't let your emotions get involved
But what happens when the siblings are assigned to a certain case?, and this case made them break every rule.
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Yet not edited and I do not own black butler
Also I'm very sorry for any errors, I try my best