The Bank of Japan December policy meeting summary is here:

In it the Bank specifically mentions its watching the risk of abrupt moves in the FX market. How to read this is the Bank does not want to see the yen rising rapidly.

Indeed you may remember last week Japan's Prime Minister was quite specific about not wanting this:

If USD/JPY drops towards 100 you can expect the first step will be 'jawboning to attempt tp get the yen lower. And, given the clear instruction from the PM intervention if this does not work.

2021 could be interesting:

The Bank of Japan December policy meeting summary is here: