Having a storied history, culture, and customs go beyond simple birthright citizenship and xenophobic behavior to enforce said culture and sense of identity. The US, for all its faults, exemplifies how unnecessary it is to rely solely on where you were born— anyone can move to the US, get citizenship, and call themselves “American.” I honestly cannot understand what “connection with the land” even means in reality. Most people aren’t farmers, and land has no inherent culture. People do, and culture is acquired by living in it and participating in it. Culture also changes overtime and is, like the earth itself, for the living.
This idea that for some reason other human beings cannot embrace, be a part of, and contribute to existing culture simply because they were born in a different country is flagrantly absurd. It’s also how people who are born somewhere, but don’t “look the part” have to fight an uphill battle to prove they are.
So yeah, Japan could be called Japan if people who live there are culturally Japanese, participate in shared culture, and contribute to it. I am also absolutely aware that isn’t possible by any reasonable means currently, but it doesn’t change the fact it should be.