Oppabiz revolves around the lives of two women, Shin Hye-joo (played by Choi Jin-hyuk) and Kim Hye-joo (played by Park Ha-na), who become embroiled in a complicated web of relationships, family dynamics, and rivalries. The story centers on Hye-joo, a talented but struggling businesswoman who tries to make a name for herself in the competitive world of marketing. Her life takes a dramatic turn when she meets her "oppabiz" (older brother's business partner) and becomes entangled in a romantic and professional relationship with him.