Well, yes. Japan as a nation is a net creditor. Net creditor don't generally struggle when paying back their debts. The question of where the money will come from has an obvious answer. If the US was a net creditor then the story would be completely different.
Japan's currency is in the toilet. They are struggling.
The value of a currency has nothing to do with how that country’s economy is doing. It’s mostly a factor of international trade. That has nothing to do with debt ratios.