The history of Reiki is a topic of much debate. It would seem that in its travels from Japan to the West, the history of Reiki underwent certain modifications to make it more acceptable to the Westerners.
Most notably, Mikao Usui, who is now believed to have been a Buddhist monk, was searching for knowledge that enabled Jesus to heal by the laying on of hands. The idea of healing by projecting energy through the hands is not new to Japan. In fact many forms of this style of healing have existed in China and Japan for thousands of years.
It seems that around 1914, Mikao Usui was meditating near the sacred mountain Kurama Yama in Japan and it is shortly after this that Reiki emerges in its recognisable form. In 1925 a retired naval officer and doctor Chijiro Hayashi studied with Mikao Usui and became a Reiki Master Teacher and set up a clinic of his own. This is where Hawayo Takata comes into the story. She was diagnosed with cancer and came to Dr Hayashi's clinic and was cured from cancer. She brought Reiki to the US in the late 1930s.
Perhaps the greatest gift that these three people have given to the West is a secular form of healing that is accessible and practical for very ordinary people to use very effectively.