Is it just me or does it seem like Japan doesn’t feel super interested or attached to the other asian nations very much? (not that that’s bad, I’m just wondering if it’s been acknowledged)

I think it’s more to do with your second assertion. It’s not
that he’s not interested in them. He amicably interacts with them quite often
and will even do favors. However, they’re not super close either. They get
along, but you can still see historical rifts affecting their present relationships,
which is seen in their civil but not super close relationships in the manga.
(e.g., you still have the whole controversy and debate over Japan apologizing
for the use of comfort women going on today).

For the most part, it goes unacknowledged. There is one
specific panel that offers a much different outlook, though. Post coming up
tonight!