<p>This study investigates the characteristics of marriage and fertility transitions in Japan, South Korea, and China using historical demographic data, revealing a tightly coupled relationship between marriage and childbearing across all three societies. Fertility decline consistently coincides with transitions in marital patterns, with three distinct stages observed during their progression into ultra-low fertility. The first phase features a rapid decline in fertility accompanied by shifts in age specific marriage patterns. The second phase combines continued fertility decline with marital transition and a rising lifetime unmarried individuals. The third phase exhibits adeceleration in fertility reduction and stabilization of marriage patterns. Empirical date identify Japan as being in the third phase, South Korea in the second, and China in the first phase. Tempo effects emergeas a pivotal driver of low fertility levels in all three countries with the strong marriage fertility nexus exacerbating the demographic consequences of these effects. To effectively address the challenges of ultra-low fertility, the three societies must prioritize interventions targeting the rise in unmarried rates as a central driver.</p>