Hakoiri Musume Desuga, Keiyaku Renai Hajimemashita

Iroha has stayed single all 23 years of her life. Her mother, who single-handedly raised her and gave her the life she has, has arranged a marriage interview. As a dutiful daughter, she agrees to attend. But before her life as she knows it is changed completely, she secretly plans out a final act of defiance. For her plan to be realized, she needs an accomplice. And thus, she makes a proposition to Kashiwagi, the best-looking guy at her workplace. Met with blunt refusal, Iroha initially becomes dejected. Then... not a moment too soon, Kashiwagi changes his mind and ends up agreeing to her plan. His request in exchange? To enter a contract relationship with him and become his "girlfriend" for the time being! (Source: MangaPlaza)