The story of Reiki starts in Japan with Mikao Usui (1865-1926). After many years of study and preparation, Usui Sensei underwent a 21 day fast on Mt. Kurama where he experienced enlightenment. At the same time, he received the gift of healing. He dedicated the rest of his life to healing and teaching. He left behind an organization, the Usui Reiki Ryoho Gakkai, and 21 teachers to carry on his work.
Chujiro Hayashi (1880-1940), a retired naval officer and medical doctor, was one of Usui's students. Hayashi established a clinic where only Reiki was used to heal. He also taught Reiki and started his own organization. One of his students, Hawayo Takata (1900-1980), was in a unique position to bring Reiki to the West, being born in Hawaii of Japanese parents.
After World War II, Mrs. Takata found it necessary to modify the teachings of Reiki to make it acceptable to the West. She did not train teachers, however, until the last few years of her life. These teachers were from varied backgrounds and did not receive the same information.
Many different versions of Reiki have emerged. Some mixed with New Age teachings and personal revelations. In one form or another, Reiki has spread around the world and grown in popularity.
Today, they are many dedicated individuals researching the origins of Reiki in an attempt to discover the Reiki that Usui Sensei taught. However, students at advanced levels were taught individually and the information provided most likely varied with the student's background and ability. Therefore, it is unlikely that one "true" teaching will ever be discerned.
In general, the various versions of Reiki all teach hands-on healing, the Reiki precepts, symbols, distant healing, and an attunement. However, they teach different ways of doing hands-on and distant healing, various different symbols, and there are many different attunement methods.
The prospective student need not be too concerned about the different approaches to Reiki. It is important for the student to find a teacher that they are comfortable working with. After taking a Reiki 1 class, the student needs to give themselves Reiki daily for at least 20 minutes, an hour is better. It is the on going practice of Reiki, that brings results.