Family offices are often introduced as wealth-management solutions for ultra-high-net-worth families. This framing is incomplete. Drawing on family-office research, family governance, agency and stewardship theories, socioemotional wealth, and boundary-organization theory, and integrating accumulated insights from Korean family-firm and chaebol governance research as well as Korea-specific institutional conditions (the 2024 Corporate Value-up Program, recent Commercial Act amendments, and the family business inheritance deduction), this teaching case argues that family office design is first a governance architecture problem. The case follows Min-ji Han, a second-generation chief financial officer in a disguised composite Korean family business. After a pending minority share sale creates substantial liquidity, she must recommend whether the family should adopt a lean external-adviser hub, a fully internal single-family office, a bank or securities-firm multi-family-office platform, or a phased hybrid model. Students evaluate eight criteria—governance clarity, stewardship fit, agency-risk control, capability fit, scalability, confidentiality and cyber resilience, cost discipline, and launch timing—and apply a weighted scoring model with sensitivity analysis. The case contributes a decision-rights framework for designing family offices around family needs before selecting investment products or service vendors, supported by a twelve-month implementation road map, methodology appendix, and 90-minute and 180-minute teaching plans.