If they keep this up they'll unite not only all of asia against them but the entire eastern hemisphere.
In the 1400’s China was the worlds great super power. China dominated the pacific but then for some strange reason turned inward. So their claim goes back to the brief time when they dominated the region. Seems like a pretty weak claim to me, but might makes right and China has a lot of might.
Who knows?
They might even give it some happy name like “Greater East Asia Co-Prosperity Sphere”.