It doesn't make sense. Waaaay too much hate between countries in Asia. Asia is not a united front. Which is not as much the case in Africa, and even the African Union isn't really all that powerful, there is very little integration between the African states. In fact the only thing in common between the European Union and the African Union, is the word "Union".
China and Japan hate each other, Japan and North Korea hate each other, Japan and South Korea relationship is complicated, South and North Korea hate each other or dislike each other depending on who is president in South Korea , Vietnam and China don't like each other. Indonesia and Malyasia its complicated. India and China don't like each other. India and Pakistan hate each other, Bangladesh and India its complicated, India and Sri Lanka dislike each other, Pakistan and Afghanistan its complicated, Tajikstan and kyrgizstan don't like each other. Saudi and Iran stuff is complicated. So no real unity.
Japan's best relations are with countries outside of Asia, in many ways Japan is closer to the US than any Asian country, Similar things could be said about South Korea.
Overall you are misjudging the conditions need to create any union. You have to look at how the European Union was created in the first place, and figure things out from there, with little steps.