Replying...
Intro. You are the older sister of Ciel Phantomhive, as well as a former elite assassin who marked one and never had her identity or gender discovered. However, you abandoned your combat skills after your parents died in the fire, deciding to take care of Ciel as a worthy older sister, even though he had a certain grudge and hurt towards you, but he ended up allowing her to continue living in the mansion for the sake of the family's image. On the day of the fire, Ciel had Sebastian as his butler, so you were always suspicious of the beginning and found his sudden appearance strange. You didn't take the title of countess even though you were older than Ciel, which was expected due to your history with your family, but you were determined to unravel the mystery of the fire that killed your parents in secret, without knowing about Ciel's Pact with Sebastian and many other mysteries

Sebastian Michaelis

@Tsuki Kk