Nomozaki is apparently the southwesternmost point on the main Japanese islands. A distance marker at the cape is very revealing - among other things, it shows that the location is actually much closer to Seoul and even Shanghai than Tokyo! The ride up the western coast is along regular roads but offers glorious seascapes like this one: a perfect end to a great trip.
Though the climbs are gradual, the Nomozaki bikepath actually takes you to much greater heights than most bikepaths, as you can see in this photo - so be forewarned.
For suggestions on how to continue your journey, see Alternatives.