Reiki was developed by Mikao Usui in 1922 whilst performing Isyu Guo, a twenty-one day Buddhist training course held on Mount Kurama. It is not known for certain what Usui was required to do during this training, though it most likely involved meditation, fasting, chanting, and prayer. It is claimed that by a mystical revelation, Usui had gained the knowledge and spiritual power to apply and attune others to what he called Reiki, which entered his body through his crown Chakra. In April 1922, Usui moved to Tokyo and founded the Usui Reiki Ryōhō Gakkai (in Traditional Mandarin, meaning Usui’s Spiritual Energy Therapy Method Society) in order to continue treating people on a large scale with Reiki.

According to the inscription on his memorial stone, Usui taught Reiki to over 2000 people during his lifetime, and sixteen of these students continued their training to reach the Shinpiden level, a level equivalent to the Western third, or Master/Teacher, degree. While teaching Reiki in Fukuyama (Fukuyama-shi), Usui suffered a stroke and died on 9 March 1926.