Japan's interest on the public debt is around $250B/year, or around 5% of GDP.
5% is a higher percentage than most countries (U.S. is around 2.5%) but less than, say, Greece at the height of their crisis. And Greece ended up not defaulting and not devaluing their currency (obviously, being in the Eurozone).
$250B is around 25% of the annual government budget for Japan. Again, this is higher than most countries but manageable.
Additionally, 92% of Japan's sovereign debt is held domestically. This means that the interest paid on those bonds don't go to Wall Street or Beijing but rather to Japan's own banks and pensioners. As a comparison, 47% of the U.S. debt is held by foreigners.
In summary, Japan is in absolutely no danger of defaulting under current conditions, without even taking the additional step of "printing more money" to pay its future debts.