Yomega Kiss

Yomega Kiss summary:

Super serious and uptight high school student Koutaro Suzuki and his obnoxious gyaru kouhai Sorako Mozu get along like cats and dogs. She spends her days tormenting him, while he spends his days getting outraged by her. However, the two of them share a secret...that they're living together as fiancés!! Under the condition that Koutaro marry Sorako, who comes from a wealthy real estate family, they've agreed to buy his father's company and save it from going under!!
Having to deal with Sorako, who uses this and that (and you know what) to torment him, can Koutaro make her yield and successfully marry her?!