I like many of these "occupyng Japan /and Philippines" etc as fantasies-respectfully to you all BUT reality wise a quick/successful nearly bloodless type of Special Forces/naval/air combined assault that DOES NOT involve mass civilian casuaties-they're our people afterall-that retakes /reunites Taiwan will be enough to have 5EYES/Japan shitting their pants in fear/consternation a long meat grinder in Mindanao(these Philipine Muslims are no pushover and have the experience of over 150 years of anti-infidel resistance that the USA/Muslim world will love to drag China into an endless quagmire.Also Japan is no cakewalk and despite 70 years of cucking by west can resort back to the murderous wako that's at their hearts and will be revived by USA as a tool against China-now Nippon HAS to be warned off in no uncertain terms that Japanese military involvement in aircraft/ships/troops in Taiwan itself will be met with full scale deadly force and possible incineration of Japanese bases in Shikoku/Kyushu/Okinawa-that's the type of ecenario China is up against-win all or lose all.
China had >1000 years to colonize both, historically China doesn't bother people who doesn't bother China.
Having said that Chinese culture also hold revenge as a virtue, and historically China always, eventually, went after those who did attack China. Japan did, NATO did in 1998, Philippines haven't, yet.
But this is about practicality, practically both are islands and this is the 21st century, neither are going anywhere, nor are they attacking anyone without US supplies. Deal with the US and China has plenty of time to decide what to do with them based on if they participated.
In term of occupation, that's stupid, if your goal is to integrate the people, you need to save them from an enemy, not be the enemy. If you want to take the land, there are nukes or just AI drone swarms, if you want to punish them, just destroy all power plants and lock them in the 19th century. No option requires ground ops. Remember this is would only be relevant after dealing with the US, China's option pool would be a lot bigger than Russia or Israel.
Of course the current Chinese government won't do neither and will prefer if both remain neutral or, if they choose not to be, be made neutral by minimal force. Whoever come after Xi however might not be as nice, and Japan has a lot of blood debt to repay.