Nikkei has out performed SP500 over last 5 years.

YTD:
SP500: 18%
Nikkei225: 25%

5YEAR:
SP500: 85%.
Nikkei225: 88%

PE 25 vs 16 too

Is the weak yen reason for the influx of cash in Japanese stock market?

Some Japanese companies definitely do well and grow fast but even legacy companies such as Toyota stock rise quite substantially.
Afaik mostother car makers stock is down over the last years.