Tokyo, metro or subway or underground: Let's go for a ride and a tour of Tokyo's fascinating and ultra modern subway (metro/underground), Japan. Vic Stefanu, vstefanu@yahoo.com. Tokyo, is one of the 47 prefectures of Japan, and is both the capital and most populous city of Japan. The Greater Tokyo Area is the most populous metropolitan area in the world. It is the seat of the Emperor of Japan and the Japanese government.