On Dr. Usui’s memorial stone, it says "In Sept of …(1921), the devastating Kanto earthquake shook Tokyo. Thousands were killed, injured or became sick in its aftermath. Dr. Usui grieved for his people, but he also took Reiki to the devastated city and used its healing powers on the surviving victims."

The memorial understates the damage caused by this immense quake. The Great Kanto earthquake (also called the Tokyo quake) of 1923 occurred at noon on Sept 1 of that year. The seismic scale of the time only went up to 6, but based on the degree of damage, the earthquake was likely at least 7.0, and some reports put it at 8.3. Official reports say the quake lasted between 4 and 10 minutes. In one place (Misaki) the amount of vertical movement was 24 FEET, although it afterwards sunk back to about a change of 5 ft. The earthquake created a tsusami (tidal wave) 30 to 40 feet high which crashed onto shore about 5 minutes later. Because the earthquake struck as lunches were being cooked throughout the city, fire was a severe problem in the mostly wooden city.

The death toll was not merely thousands as stated on the memorial but 142,000 dead and missing, and almost 100,000 injured.  576,000 to 694,000 buildings in the region were completely or partially destroyed most by quake, tsunami or fire. The aftermath was also incredibly difficult. It was estimated that 45% of the population lost their jobs. 

The Kanto Earthquake was the beginning of greater fame for Mikao Usui. On the Usui Memorial it says "Dr Usui grieved for his people, but he also took Reiki to the devastated city and used his healing powers on the surviving victims. His clinic soon became too small to handle the throng of patients." Because of his compassion and willing to help others in the aftermath of this event, Usui’s fame spread thoughout Japan.