This study established a population projection system for analyzing demographic change and supporting policy research to address unprecedented demographic transitions of ultra-low fertility and a super-aged society. We introduced the Parity Progression Ratio (PPR) method to incorporate first marriage rates as an explicit policy variable, extended life tables to age 130 to strengthen the analytical foundation for the oldest-old population, and constructed an integrated population-household projection framework based on marital status transitions. The 100-year projections under different first marriage rate scenarios confirmed the long-term cumulative effects of marriage support policies, while emphasizing that population aging cannot be mitigated by fertility policies alone, highlighting the importance of adaptation policies such as extending healthy life expectancy. This study is significant in establishing a framework for microsimulation integration that enables flexible responses to diverse policy scenarios.