Ayakashi Kazoku no Youko Reijou, Onmyouji to Seiryaku Kekkon suru

The ayakashi, once driven out of the public world by the exploits of Onmyoji (exorcists), now live hidden among humans. The Hasumi family, who run the long-established restaurant "Hanamushiro," are also a clan of fox spirits skilled in shapeshifting. A marriage proposal has been made to the Hasumi family. Moreover, the woman they wish to marry is not the younger sister, the child of the legitimate wife, but Sena, the eldest daughter born to a concubine. The prospective groom is Kedoin Itsuki, the head of a prestigious family that enjoys the trust of the government in the imperial capital. Her father is delighted at the prospect of a connection with a noble family, but this marriage has a major problem. The Kedoin family is a lineage of Onmyoji, the sworn enemies of ayakashi! If her true identity is revealed, she will be exterminated!? A tense newlywed life has begun!

(Source: Shueisha, translated)