Ω Reijou, Jouyoku no Ori: Taishou Kenran Omegaverse

Overview

It is the Taisho era. Sayo Tenkadera is treated coldly as a "caged bird" by her family, one of the most prominent zaibatsus in the country. She secretly harbors feelings for her cousin Eiji, from a distant branch of the clan. But then it is discovered that Sayo is a rare "latent omega," and she is ordered to marry the alpha Shogo, the second son of the Sanada clan, in a political marriage for the sake of her family. In the cage that is the family mansion, the lady drowns in forbidden "love" and "desire." It is a lusty historical omegaverse story about a prestigious Taisho clan! (Source: Akita Shoten, translated)

Source: AniList