There are two power transitions, one from the US to China in global dimension, and the other from Japan to China in regional dimension in East Asia. We argue that so-called ‘dual power transitions‘ in East Asia exist as an important region-specific factor to disturb regional economic integration. Moreover, those have resulted in mega FTAs’ domino worldwide. Japan has played significant role to accelerate such FTAs’ domino, after Korea pulled the trigger by Korea-US FTA, as Japan is one of the super powers composing dual power transition. Japan’s participation to the TPP negotiation prompted China’s reaction to call not only Korea-Japan-China FTA but also RCEP. The mega FTAs’ domino continued to Japan-EU FTA and eventually US-EU FTA as well. Japan’s intention to participate to mega FTAs is mainly to lead global rule making by means of TPP and Japan-EU FTA under circumstance that WTO-based multilateral market opening has stagnated almost a decade. No doubt, Japan will play certain roles in mega FTAs since it propels three mega FTAs simultaneously while it also faces to harsh domestic protests regarding the opening of agriculture goods market.