To prove I'm not dead,
The year is 2056, and the standoff between Japan and the continent continues. The sovereignty of the Senkaku/Diaoyu, Dokdo/Takeshima Islands, and island of Taiwan is question. Increasingly however, Beijing threatens that when the situation is realized Japan will be brought 'in line' with the rest of Asia. Japan, for its part, is increasingly worried that its LDP-run democracy, sovereignty, and independence are being called into question.
In a world where the European Union has evolved through many forms but remains essentially functioning to the present day (with no single defining Brexit but instead a long history of 'half in, half out' British governments), Asia has followed suit. India and China, despite their differences, have found that by integrating their economies the speed of development has at last allowed both to outdo the U.S. in sheer economic size (though the aging U.S. remains quite a bit ahead in GDP per Capita). There's quite a bit of healthy competition between the two, but their joining forces convinced many more states to join in. A single bank, currency (to compete with the Euro and Dollar), unified armed forces, and a loose set of basic laws above even national ones, followed. The name for this union, containing roughly half of humanity, came from one of the ancient Sanskrit names for the continent (roughly equivalent in meaning to the old Anglo-Saxon's 'Middle Earth') - Jambudvipa (閻浮提 'Yanfuti' in Chinese, 'Enbudai' in Japanese). The Jambudvipa Collective soon became large enough to self-sufficient; though member states function essentially as a single economy now, trade with the outside world has been essentially ended.
Japan (which has surpassed the U.S. in GDP per capita but has a much smaller economy overall) had no interest in joining a Beijing-Delhi co-dominion, and has been horrified at the loss of relative power to the continent. Another non-joiner, has been the Republic of Taiwan, which dropped pretenses of unifying with the mainland two decades back. Taiwan is undergoing a bit of a dramatic change; nationalism and self-love of a uniquely 'Taiwanese' identity are surging, and Taiwanese (Taiwanese Hokkien written with a combination of Characters and Bopomofo, similar to how Japanese is written) has replaced Mandarin as the official language. On the mainland, the Chinese 'Dialects' (except for Cantonese which is going plenty strong) are being squashed, and the non-Han minority languages are going the way of Irish, but Taiwan's political spectrum is united behind the carving out of a new identity.
The U.S. is still treaty-bound to protect Japan (though Washington makes a point of saying it will not intervene in a conflict if Japan is the initiator), but the protection of Taiwan is managed essentially independently by Tokyo. Though the Jambudvipa Collective's army, numbering nearly six million active troops*, is the largest in the world, Japan has a few tricks up its metaphorical sleeve. Japan went nuclear a few decades ago. And, this being the future after all, Japan has the world's most advanced robot army. Japan's navy is on closer footing of course, but still a bit behind. Even pushing nuclear technology aside, Japan has enough biological weapons stored up to kill a few hundred million. Japan's economy, though long seen as one of the most stagnant in Asia, has in the last three decades accomplished Meiji-esque levels of catch-up.
It's a rather State-Capitalist, Single-Party-Democracy World (Japan still has the LDP, China's Communist Party has a few alternatives but is still assured of election victory 95% of the time, and India may have sidelined the Congress and BJP but there's a new topdog in Delhi too). Global Warming has made significant changes to the Earth atmosphere, but recent efforts have meant that its not going to get much worse. The moon is dotted with settlements, and military bases have been established as far out as Pluto. The Internet is less and less one piece, with paywalls and censorship making it work increasingly differently in different countries. Though the world increasingly looks divided into large blocs* which operate outside of the U.S. system, American culture (or at least American Culture from roughly 1950 to 2020) continues to be a powerful influence around the rest of the world. Increasingly, mainland Asia (with its homegrown fast-food restaurants, unnecessary love of highways and suburban sprawl, and an over-the-top 'can do' attitude) shows influence of a fun-house mirror version of U.S. culture.
Amidst much larger powers, Japan finds itself increasingly isolated but up to the challenge.
*(Former Russia, North Africa, Central America, and of course Japan-Taiwan being the main exceptions)