If you are traveling in Osaka, you will probably be in transit at Osaka Station at some point. Perhaps not as appealing visually as the resurrected Tokyo Station, Osaka Station nonetheless is a modern hub of Osaka, Hyogo and its greater surrounding area.
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I consider a hub a central location for a major entity, core traffic point and operations facilities.
It is true that if you want to go inland towards Gifu, the heart of Japan, Nagoya is the stop where you need to transfer. And if you want to get on Shikoku, Okayama is your hub.