Kochi City in Kochi Prefecture,
Shikoku. It has a lot going for it. It is a very livable big city. I'm like you, I don't like big cities, so I don't say this lightly. Go 20 minutes out of town (easy to do as it is a "small" big city and you are in the moutains, at the beach, or on the rivers. No snow to speak of, so your winter sports itch will need to be scratched elsewere. However, Kochi has some of the best surfing in Japan. Kochi City has a nightlife to keep you happy, an airport, ferry terminal, train line and overnight buses to Osaka and other points. The only drawback is it is a little out in the boonies, making transportation a little pricey. However, the living is easy and the prices lower than in similar cities on Honshu or parts of
Kyushu. However, unlike other places in Japan, Kochi City, and Kochi in general, is not a case of nature fighting to survive in a concrete jungle, but more mankind trying to keep nature out of the cities. Also, and this is important to me. It is not flat. Look past the buildings (of which there are not many) and you have mountains, or the sea. I can't stand cities where the skyline is just an unbroken line of rooftops. Good luck