I think this is quite clever on South Korea's part. They know that the American plan to contain China has been a complete failure, so instead of going all-in with a fading American strategy, they're looking at alternatives at a time when China is receptive. The other neat part about this is that the main American support to South Korea is that American troops can help defend them in case North Korea attack. However, China is technically North Korea's ally so they can prevent such an attack altogether.
This, on the other hand, is just dumb. The only countries that might be receptive to Japan's message are Taiwan and Philippines, and nobody really cares about the opinions of either of these countries. Hell, I don't think that even the people living in those countries care about their government's opinions. And just about every country that does cares about this subject is going to be just that much more angry at Japan; this being especially true of South Korea. It's just a terrible own goal at a time when Japan needs more friends.
Oh, and I should note that this year, China invited KMT veterans to attend the parade. The DPP has threatened to revoke the pensions of anyone who does this.
