Since when is East Asia considered "Western"?

I live in a Japanese city with a US military base and trust me, the only Western thing here are the few bars that cater to them.

Among the many definitions of "Western" is the original sense of "First World", encompassing members of the geopolitical bloc centered historically on the US.

If the world splits into a China bloc and an American bloc, Japan would almost certainly join the American bloc, right?