It is often highlighted that from the mid to late Edo period, fathers in almost all social classes were earnestly involved in childcare. However, the modernization and industrialization of the Meiji period positioned Japanese fathers not as caregivers, but as economic providers. The resulting absence of fathers from home continues to be one of the crucial contemporary problems in Japan. This paper examines why Japanese fathers in the Edo period were more engaged as caregivers and how their involvement in childcare became inhibited with historical change. This examination leads to an identification of important sociocultural factors influencing fathers’ involvement in childcare. Four key factors facilitating fathers’ involvement in childcare were identified. The first factor is the social environment in which fathers pay attention to the survival and maturity of their offspring. The second factor is the ideological belief that embraces everyone as co-parents. The third factor is a method of childrearing emphasizing the importance of fathers’ physical interaction with children from an early age. The fourth factor is the existence of means to share norms and values surrounding fathers’ childcare. Understanding these sociocultural factors in the light of current research, it can be said that the Edo period is a unique age in which paternal behavior emerged in almost all fathers. The findings suggest that fathers’ involvement in childcare is “nature,” “nurture,” and their dynamic reciprocity.