Osaka is nice, its easy and cheap to get to other places like nara, kobe kyoto, himeji castle, okayama (maybe). you can travel by local trains with a ju-hachi kippu fairly cheaply.

if you are outside japan you can buy a shinkansen pass which cannot be bought in japan. it would be a good thing to get if you want to travel the country for the time you are there.

i lived in Takamatsu on Shikoku, great place to live. not much to see, unless you just like rural japanese landscapes. Pretty much the opposite of Tokyo. which is great to visit not so much for living there.

Naoshima is my favorite place in japan.

Osaka - namba, dotonbori and shinsaibashi are pretty interesting.

Tokyo - yasakuni shrine, and all the obvious places are good.