One thing to keep in mind is that the Nikkei 225 (like most indices except the German DAX) is a price index, and, (like the Dow) a mediocre one at that.

A better index is the Topix, and that’s available in a total return (and net return) variant (that is, including dividends before (or net of) taxes)).

A fairly low dividend yield would suffice to make the total return index exceed the 1990’s high by now. (It’s not trivial to find the data to confirm this for free.)