Ayakashi Kazoku no Youko Reijou, Onmyouji to Seiryaku Kekkon suru

In a lawless age over a millennium ago, yokai terrorized the streets, leaving victims scattered in their wake—until the emperor ordered onmyoji to purge them from the human realm. Centuries later, the aristocratic Ren Sui family, proud proprietors of the esteemed restaurant Hanamushiro, receives an unexpected proposal: Keto-in Iitsuki, the powerful head of an imperial bloodline, seeks not their legitimate daughter, but Setsuna, the eldest child born to a concubine. While her father celebrates the political alliance, this marriage hides a perilous secret—the Ren Sui clan are yokai living disguised among humans.