The formation of yen bloc did not result in the economic and monetary integration of East Asian economies. Rather it led to the increasing disintegration of East Asian economies. Compared to Japan, Asian regions and countries had to suffer from higher inflation. In fact, the farther the countries were away from Japan, the more their central banks had to print the money and the higher their inflations were. Moreover, the income gap between Japan and other Asian countries widened. It means that the regionalization centered on Japanese yen was destined to fail, suggesting that the Co-prosperity Area was nothing but a strategy of regional dominance, not of regional cooperation. The impact was quite long lasting because it still haunts East Asian countries, contributing to the nourishment of their distrust vis-à-vis Japan, and throws a shadow on the recent monetary and financial cooperation movements in East Asia. This experience highlights the importance of responsible actions on the part of leading countries to boost regional solidarity and cohesion for the viability and sustainability of regional monetary system.