Marked improvements in cancer survival among reproductive-age women have transformed fertility preservation (FP) from a niche intervention into a core pillar of survivorship care. In Japan, national policy milestones—including the Third Term of the Cancer Control Promotion Plan (2018) and the launch of a government-supported financial aid system for FP in 2021—have enabled rapid diffusion of oncofertility practices (including FP) across oncology services. The Cancer Control Promotion Plan has moved into its fourth term and is developing further (2023). Hereditary Breast and Ovarian Cancer Syndrome (HBOC), mostly caused by germline BRCA1/2 variants, represents a unique intersection of cancer genetics, reproductive endocrinology, and ethics. This scholarly review synthesizes the biological basis of female fertility, mechanisms of gonadotoxicity, and the evidence supporting established and emerging strategies for FP, with a specific focus on the care of HBOC patients. We integrate national Japanese data and programmatic advances, highlight the safety and feasibility of assisted reproductive technology (ART) in BRCA carriers, and delineate ethical and genetic counseling imperatives, including timing of risk-reducing salpingo-oophorectomy and the role of preimplantation genetic testing for monogenic disorders (PGT-M). We conclude by outlining priorities for registry-based evidence generation, equitable access, and multidisciplinary coordination that will determine the next decade of practice.