In 1923, the Great Kanto Earthquake struck the region and Tokyo was shattered. Over 100,000 people were killed, and the infrastructural damage exceeded anything the city had seen to date. The yearly anniversary of the quake, September 1, is now known as Disaster Prevention Day.
Source: https://www.discoverwalks.com/blog/tokyo/10-most-famous-historical-events-that-happened-in-japan/