I am considering starting index investment with the new NISA for the purpose of retirement asset formation. I am currently 33 years old and plan to make a monthly deposit of 0.05 million yen. I was thinking of investing in the S&P500 or US stocks (VTI), but after watching Buffett Tarou's YouTube video, I am hesitant because there is a high possibility that US stocks will slump in the next 20-30 years. I would appreciate your advice.