Here is a youtube channel of a guy who likes to follow the storms in that area:
CAt 5? impossible maybe at some point in it’s life?
Japan Meteorological Agency:
How this one was felt across Japan:
The intensity dots are linked such that you can keep zooming in on the reports at their individual source locations.
While this one was well off-shore and not felt too strongly on Honshu and Hokkaido, the "big one" of 2011 was preceded [by only a day or two] by several strong off shore EQs, a couple of them 7+.