I Became The Rumored Illegitimate Princess

I reincarnated into a grimdark fantasy’s villainous noble house.
And not just anyone-I’m the illegitimate daughter of the duchess, who’s rumored to be a half-wit and unable to even walk properly.
“Who are you calling ‘big brother’?! Address me as ‘young master’!”
But everyone’s been deceived by my mother’s lies.
The illegitimate child isn’t me, it’s the eldest son of the house, Boris Rohia, the little tyrant of House Rohia who used to torment me relentlessly.
“Lately, I’ve been thinking… we might be a bit alike.”
Even my second brother, Joseph, who’s the only one that ever looked out for me, is destined to become the main lead’s worst nightmare and a top-tier psychopathic mastermind.
“Hahaha! At last, it’s born! [Materia] !”
And to top it all off, I’m actually the prophesied savior of the world…
…except because I’ve been mistaken for an illegitimate child, the newborn youngest sibling, Yubel, is believed to be the savior instead.
‘What the f*ck.’
The whole world is out to screw me over!
But I won’t go down without a fight.
With a smile, I grit my teeth.