To me, it's very reasonable that Japan should definitely get directly militarily involved with Taiwan so that China will have a great reason to directly bomb Japan. In fact, I wish Japan would be even more reasonable and immediately launch a full scale invasion of China today so that they can be definitively defeated and annexed.
I think you misunderstand something essential. To be anti-foreigner is a completely different thing from being insular. To be insular is to be very ignorant of foreign ways and means. To not understand the methods they use to infiltrate, undermine, corrupt, or attack you. And hence to not understand how best to defend and counterattack. Someone who is insular tends to only understand the ways and means of those in the culture they grew up in. Japan and South Korea are very insular.
One can be both insular and anti-foreigner. Many Westerners are. Those ones typically resist foreign influence in futility and then lose like the MAGA types.
Then of course you can also be insular and pro-foreigner. Many libshit Chinese who have not traveled, lived, or worked in the West very much are. They do not really understand the West beyond flattering but incorrect generalizations, and so they aspire to, admire, or even worship it.
You can be worldly and pro-foreigner, like the libshits that have the money and time to travel extensively, live/study/work abroad, and understand the world abroad but still admire and worship the West. Usually because it's just a dressed up form of worshiping what they perceive as superior and looking down on what they perceive as inferior, rightly or wrongly. These types are likely to blow in the direction of the wind and change their orientation when they see the fortunes of the two groups have sufficiently reversed. I imagine a majority of Hong Kongers and Singaporeans fall into this category.
Lastly, you can be worldly and anti-foreigner. You have the time, upbringing, education, training, and/or resources to understand the foreigners and yet still understand they are your greatest adversary. You know their ways and means and how best to defend or counterattack. I suspect a reasonable proportion of key decision makers in CPC likely fall into this category.