It's pretty simple. It's been a rather long time since Japan has had that kind of stock market and with the kind of progress Japan's making in the automotive industry and what not, it won't take much for Japan to beat the very peak it reached in the 1980s. It is an ever developing country and it's sure to hit and cross the stock market it reached in the 1980s.
While the stock market of Japan was at a peak in the 1980s, it is possible for it to reach that peak again. Why? The economy of Japan is steadily improving, and more foreigners are becoming interested in Japan, as they were in the 1980s. This would increase exchange of Japanese stocks, improving the stock market. The current prime minister, Shinzo Abe, and his plan "Abenomics" introduce new policies, which could help the Japanese Economy, and boost the stock market.
Japan's stock market will beat the peak it reached in the 1980s. It seems as though Japan's economy has been growing and expanding as the population grows. Although the American stockmarket crash has impacted many countries worldwide, I feel that Japan's stock market will continue to grow and expand as they utilize their resources and continue to create the technologies and products that companies worldwide desire. This will increase the strenght of their stock market and take them past their 1980s peak.
The 1980's were a very good time in Japan. The national economy had reached great heights after decades of Japan's emergence as an economic powerful, and it seemed that the country had a very bright future. But sadly, those days seem to be gone. It would be hard to imagine Japan ever returning to that former state, unless it were to discover some substantial new natural resources, or to somehow regain its former technological edge.