I have a slew of thoughts I still haven't completely fleshed out in a publicly sharable form yet, and are from the perspective of a western-raised person, but the summary would probably look something like:

- Most of your socially active friends will most likely leave within 2-3 years of arriving

- If you were raised in the west, family and culturally similar communities are likely quite far away (both in flight hours and timezone changes)

- It is notoriously hard to break into Japanese social circles, regardless of language competency. Acquaintances are easy, but I'm talking about deeper connections.

AFAIK Japan is a high-trust, high-context society. It is difficult to break into social groups or make new acquaintances, while the infrastructure necessary for living a "solitary" existence (supported by service-providing strangers) is extant and quite sophisticated.