i'm not so sure tbh
taiwan is realistic because taiwan as a country only really became a thing when kmt remnants made it their last holdout after losing the rest of china to mao. taking taiwan basically would be the final conclusion to the chinese civil war.
think about it like this: imagine if after the end of the american civil war, the confederates all fled to alaska, dismantled alaskan state intitutions and turned it into a de facto independent nation state, and stayed in power there until the current year, while still calling themselves the confederate states of america and laying claim to all mainland american territory while denouncing the USA as illegitimate. that's what taiwan is to china, that's why they're such a thorn in the CCP's side.
japan though? much bigger, much more powerful, much more well connected internationally, much more foreign and different from china than taiwan, and unlike taiwan, the ccp has no obvious and legitimate claim or casus belli against japan. and even inside china, there isn't much motivation or interest in war with japan. they're more likely to drum up some border conflicts with india, or further push their hegemony over central asia, than they are to invade japan.
