To be serious for just a moment - from a historical chart it looks like the Nikkei declined or was essentially flat until 2012, but has risen steadily for the last decade. I’d be interested in seeing what total returns look like for someone who spent the last 30 years making monthly contributions to it.
Coming right up ... this ignores any dividends and focuses solely on the stock price of the Nikkei 225.
Let's assume starting in January 1990 you invested 1,000/mo in the stock market. Every year the amount you invest goes up by 3%, so that in 2023 you are investing $2,652.
You would invest a total of $684,805 and you would end up with 1,436,044. Your rate of return over that time period would have been about
4.68%/yr.
In the last 10 years the index tripled to return to its mid-1990 pre-crash value, so your return on investments around that starting point would be close to zero. Anything else starting below that ended up positive, but keep in mind there was a long wait and your return was likely negative for the first 15-20 years.