Henkyou Mob Kizoku no Uchi ni Totsuidekita Akuyaku Reijou ga, Mechakucha Dekiru Ii Yome Nanda ga?

Ragna has reincarnated as the third son of a noble family with lands in the frontier. Thrilled at the prospect of living freely in another world without the responsibility of inheriting the family estate, his excitement was short-lived. Following the death of his father and two brothers in battle, Ragna finds himself unexpectedly taking over the family. Unfamiliar with managing the estate and continuing the family legacy, he now faces the challenge of navigating noble duties, including attending an elite academy in the capital. As if adjusting to these responsibilities wasn't overwhelming enough, an arranged marriage to a high-ranking noble's daughter is thrust upon him. This is when Ragna recalls a crucial detail about his new reality—this world mirrors that of an otome game, where his fiancée is known as the game's antagonist. (Source: Kakuyomu, translated)