Hakushaku-sama wa Otenba Reijou wo Goshomou desu

Emilia is the beloved daughter of a renowned Earl. As such, she's expected to be a lady, through and through. But the truth is, Emilia is a tomboy who likes horseback riding and hunting. One day, after slipping out to go hunting, she stumbles into territory belonging to another lord and runs into none other than the young Earl Freed. Freed finds himself attracted to Emilia's lightheartedness and offers her a proposal: a limited-time, contractual marriage. "Why don't you marry me?" Emilia accepts, but what awaits her in marriage is arguments over bloodlines, and a warning over someone's title?!

(Source: MangaPlaza)