I’ve been following this situation for awhile and I don’t believe the Japs will take this lying down. Imagine if the Japs put the same effort they put into making gadgets into their self defense force. They would probably have flying robots.
Viewed from a Chinese perspective, the line Fukuoka - Okinawa - Taiwan line is a hostile barrier that PLAN northern and central fleet units must pass through when accessing the Pacific Ocean proper. Okinawa is the center point and cork in the bottle. Okinawa is also a key base location for US forces.
Recently, the Chinese have been showing military interest (hydrographic surveys and submarine transits) in international seas around Okinawa and the PLAN has conducted fleet maneuvers in areas approaching Okinawa from the west.
In a brew-up over Taiwan, it is likely that the PLA has plans to neutralize both Japanese and American use of Okinawa as a staging base to support the ROC on Taiwan if necessary. Given their asymmetric warfare doctrine, their planning would probably call for submarine-launched commando raids that receive support from an indigenous 5th column based in Okinawa's Chinese community and perhaps would be followed up by air strikes by long range bombers. Of course, the fact that such actions would cause immediate war with Japan (and most likely with the US) means it is a decision the Chinese would very carefully consider before executing.