Cross-cultural psychology has long relied on contrasts between East Asia and North America. However, recent evidence shows that differences within East Asia are no smaller than East-West differences. Drawing on multi-country surveys along with archival data, I show that Japan systematically diverges from Korea, China, and Taiwan on personal agency, interpersonal sensitivity, and prosociality, and that these patterns are rooted in historically sustained institutional practices. I also discuss how these tendencies create distinctive challenges in contemporary Japanese social life, and how a historical-ecological-institutional approach can offer a theoretical framework for understanding psychological variation within East Asia.