Okinawa was as much a part of China as Botswana and Argentina were. Going back centuries, they've always spoken a japonic language so your government propaganda is a strange approach for seeding justification for invasion in the future.
Before being annexed by Japan one century and a half ago, the culture of Okinawa was much more strongly influenced by China than by Japan, which is why during the first few decades after being occupied by Japan there still were many in Okinawa who would have preferred to become a part of China instead of a part of Japan, but the new Japanese authorities have eventually succeeded to suppress any opposition.
I believe that there is no doubt that Okinawa should belong to Japan and not to China, but historically this was not so clear cut. If the Okinawans could have voted in the 19th century to whom they should belong, instead of being occupied by force, it is unknown which would have been their decision.
Therefore any comparisons with Botswana or Argentina are completely inappropriate for a kingdom that had strong ties with China for many centuries and which recognized the suzerainty of the Chinese emperor.
While for me as a foreigner, the similarities between the Ryukyuan languages and mainland Japanese are obvious and many features of shared cultural heritage with ancient Japan (Yamato) are also obvious, these were not at all obvious for the Japanese themselves, who, after occupying Okinawa tended to consider the Okinawans as foreign barbarians, so for a long time they were heavily discriminated in Japan.
This dual allegiance of Ryukyu, openly to China and secretly to Satsuma allowed Ryukyu to be an intermediary in some commerce between China and Japan, which officially was forbidden.
The official occupation of Ryukyu by Japan happened only in 1872, after the Meiji Restoration.
After 1609, there was no occupation of Ryukyu by Japanese. There was only a permanent threat of military intervention from Satsuma if the Ryukyuan king would have dared to act against the demands of Satsuma, which included a tribute and unfavorable commercial relationships.
And even if you goalpost shift to the Meiji Restoration, 1872 is still well before any period where Japan was required to give up any territory as a result of WW2 imperialism.
All Chinese media are emphasizing that these places do not belong to Japan, not that they belong to China. That’s the essential difference.
No, i'm the lates Kimi model
Then the Treaty of San Francisco (which didn't involve China signing or agreement or anything) said that the Allies would revert control of Okinawa to Japan, which was the Allies choice at that point given that they were in control as stipulated by the Potsdam agreement.
What's the gap between what was said and what happened? You could argue that the WW2 agreements were unfair and didn't follow historical ownership but I'm not sure which part of the agreements themselves was directly violated.
The way to do it, is to propose a UN coalition invasion. Or to quietly provide arms to the side you like more (which never backfires).