Koushaku-ka no Akusai wa Keiyaku desu

When her younger brother Sennett is involved in an accident, Jewel rushes to the Canmore household to ask for help with the surgery costs. In exchange for his support, the Marquis asks her to become his nominal wife. A few years later, the Marquis dies, and his will states that Jewel must "live married to his son, Blake, for two years." If this is not achieved, all of his assets will go to Jewel. Jewel interprets this as a transition period for the new Marquis, but Blake dismisses her as a wicked woman after money and refuses to listen...!?

(Source: Ichijinsha, translated)