Most of the people think about Osaka as a prefecture or maybe as a city, but due to the proximity of other major Kansai cities and their heavy historical and economical impact on Japan it is better to talk about the Keihanshin metropolitan area as a unified entity.
When we talk about Osaka, we shouldn’t forget about the closeness of Kyoto; the former Imperial capital of Japan for more than one thousand years (29 minutes by train from Osaka Station) and Kobe (34 minutes by train from Osaka Station) the sixth-largest city in Japan.
If you are more interested in Mother Nature and love to visit natural spaces, you will love Nara (47 minutes by train from Osaka) ounce the capital of Japan, and one of the greenest cities you’ll ever see, not only in Japan but on a global scale.
Economically speaking, Kanto with Yokohama and Tokyo is indisputably more important, but the Kansai area is way richer historically, culturally and aesthetically. So if you only want to do business in Japan you should go to Tokyo, but if you want to visit the traditional side of Japan, it is way better to stay in Kansai.
Tokyo is a must visit city because of its cosmopolitan aspect and unique magnitude . Osaka however offers way much more for someone who wants to visit the “real” side of Japan.