Nobara No Hanayome

From Shoujo Crusade:
Yamada Chizuru was a normal high school student… that is, until her mother left for a “journey” leaving her with a debt of one hundred million yen! As if that wasn’t nerve-racking enough; Kuze Mitsuru, the Umegaki gang’s Sandaime, saves her by buying her to be his fiancee!? What will become of Chizuru’s days?