Japan has been doubling down on it's rhetoric against China and the new PM has even started a campaign to get rid of the article 9 provisions in the constitution. This has inflamed tensions and China would have a reasonable case for war if Japan landed troops onto sovereign Chinese soil.
But...China wouldn't nuke them?
I mean I'm not saying they wouldn't fight back, obviously, but China has a no first strike policy. Unless Japan launches nuclear weapons first, China wouldn't launch them in the first place. This has been the policy ever since China first developed nuclear weapons. [I mean, the only other use case is that if China actually feels like they need to use it to prevent occupation/invasion of China. That's what the nuclear arsenal has been developed for, to make occupation too costly for imperialist powers. I guess technically you could argue a deployment onto Taiwan would count, but...its kinda just dumb? It's not like Russia nuked Ukraine after it invaded Kursk. Xi isn't sitting at his computer like "hehe yes I love nukes let's blow up people."]
Imo the most likely case would depend on escalation. I think if it's limited to just a conflict over Taiwan island China would probably just blockade Japan and force a deal. [I mean...they could try a ground invasion bit I don't think most Chinese people would actually want to do that given the immense resources required].
Sorry, I just keep seeing it said that "Japan will learn when they realize china has nukes this time," even by non-chinese communists. And honestly it's just...not funny? Like if it is a joke, I don't see the punchline. If it's not, then it's foolish mental behavior at best and outright callous at worse. I'd expect those kinda things from Han nationalists with the username "Yonglesgreatestsoldier" or something.
China would be better off "nuking" Japanese social media with pro-communist messaging aimed at young people, who, like everywhere else in the world, see little possible future under the current system. Like the US, Japan's capitalist system is crumbling, so the old guard is using the old tried and true method of resorting to fascism and nationalism.
I think the method of not interfering at all is far more effective. It does sound weird; but I personally think that if any attempt at meddling is made by China overtly or even just something that's not completely covert it will be taken "to the end-zone" so to speak. America will use that, more than it already does with baseless accusations against BRICS, to associate any movement related to socialism or even leftism as "Chinese-influenced" and seek to terminate it by any means necessary with a free casus belli to do so.
China doing otherwise gives them no credibility, no basis to any of their accusations. It makes them seem more estranged and gives added emphasis to the hypocrisy. It also establishes a precedent that they respect national sovereignty..more so than the IMF or what the west has to offer.
Not sure they have to interfere directly. TikTok was single-handedly responsible for waking US citizens to Israeli crimes and genocide, and that was marketed as a teenage dance video app. Lending a voice to the voiceless seems to work wonders.
By letting the propaganda spread passively you don't need to interfere or give any voices when doing such will be seen as the ultimate excuse to manufacture and attack your ideology. Leading by example, rather than spreading it. As an existing socialist state, by the way, not as a leftist group.
So far, it's been quite successful, much to the chagrin of those who wish they'd do more. I wish they could too; but I look at it more pragmatically, that this has been the most successful method so far.