https://www.mangago.zone/read-manga/doku_wo_kurawaba_sara_made/
Fits your second request, except he actually faked his tragic backstory, because our mc is a scheming villain, but none of the other characters knows that, not even his love interest (BL)
That is kind of awesome... I love that concept, thanks for the rec.
While it’s not an otome game setting(but there is a love triangle situation), nor is there a system involved (she gets stronger on her own), this one matches all you’re asking for and I quite enjoyed reading it!
https://www.mangago.zone/read-manga/oh_dear_nemesis/
stuff featuring a weak female lead (FL) in an otome setting who gains power through a system (or otherwise), eventually becoming OP. Ideally, she grows alongside a lover—who can be male or female—who is either her equal, weaker, or complements her strengths and weaknesses.
Alternatively, I’m interested in male protagonists with a "Death is the Only Ending for the Villainess" vibe, incorporating elements of angst, suffering, tragedy, and sad backstories. Yaoi or non-yaoi are both fine.
A Yaoi otome where ML is a top but acts like the typical bottom or the opposite would be cool too.