The Way to Protect the Female Lead's Older Brother

?Please be advised. This work contains somewhat sadistic expressions and portrayals of bloodshed due to the nature of the genre. We tried to capture the charm and atmosphere of the original work, but there are images that may make you feel a little uncomfortable, so please take note.
I accidentally took possession of someone in a 19+ reverse harem novel.
The problem is
that I became Roxana Agriche, the older sister of the sub-villain. My damn father kidnapped the heroine's brother.
Now, is the only thing left to meet a terrible end from the vengeance of the heroine?
But what if I can avoid that horrible development?
“I'm also interested in this toy.”
'I'll protect you until you can get out of here safely.'
The heroine's brother, Cassis Pedalian, will definitely be able to pay me back later.