In Japan, as an investor, you can trade on 3 different exchanges: the Tokyo Stock Exchange, the Osaka Securities Exchange and the Nagoya Stock Exchange.
The Tokyo Stock Exchange, or TSE, is the largest securities and derivatives exchanges in Japan and recognized as one of the core exchanges in the international financial community. It currently lists 2,271 domestic companies and 31 foreign companies, with a total market capitalization of over 4 trillion USD.
The main index is the NIKKEI 225.
The NIKKEI 225 is a stock market index of the average value of the shares of 225 Japanese companies which reflects share price movement on the Tokyo Stock Exchange.
The Nikkei average is the most watched index of Asian stocks.
The index is unweighted so smaller companies can influence the index as much as the larger ones.