Reiki is a specific frequency or band of energy used for healing and self-healing that works in tandem with Ki but at a higher vibration. Reiki originates directly from the Source (or God, the Creator, All That Is) and is channeled by that Higher Intelligence for healing (or wholing) anything, animate or inanimate.
Because Reiki energy vibrates at such a high frequency, it is normally invisible to the naked eye. However, its use can be detected using a Kirlian camera. Some people see it, typically, as a white/gold stream of energy resembling the spiral shape of the DNA double helix. Unlike Ki, which is ubiquitous and pervasive, Reiki does not flow through everyone from birth. It only flows through those who have been "attuned" to the vibrational frequency of the energy. This attunement, or spiritual empowerment, is the process by which the healing ability of Reiki is energetically transmitted from a Reiki Master to a student during a sacred ceremony that is an integral part of a Reiki course or workshop.
It is similar in nature but less powerful to a Reiki Master's spiritual empowerment, since Dr. Usui received the full understanding and the full strength of Reiki in one single empowerment, which also allowed him to become enlightened. Since he had been practicing spirituality for about 50 years at that point, he was no doubt more energetically prepared than any of us would be for such a profound experience and a vast amount of healing energy.
Many spiritual empowerments are spread throughout the various levels of Usui Reiki to allow students time to "acclimatize" themselves with each level's energy. As these sacred ceremonies "initiate" and "attune" the student to the unique vibrations of the Reiki spiritual healing energy, they are commonly referred to as initiations or attunements (attune means to bring into harmony with). When a student receives an attunement, an energetic channel is created in their body that allows Reiki energy to flow from Source through the student's energy body and out through their hands.
An illustration of the flow of energy after the attunement
This attunement "reopens" an existing channel within our energy body to our enlightened selves (our Soul/Spirit/Higher Self) that part of us that is always and wholly connected to the Source/God/All That Is. Our limited awareness of our whole existence, and our inability to perceive the full extent and potential of our being, our Soul/Spirit/Higher Self, makes it appear as if the Reiki is coming from outside ourselves, entering through the crown chakra.
As a result of the "spiritual empowerment" that occurs during the attunement, we become aware for the first time of a part of our spirit that we hadn't previously known how to access. This attunement allows students to use Reiki's healing energy for themselves or others immediately after receiving it. Because this healing energy comes from an inexhaustible Source (God/Creator/All That Is/The Universe), they will be able to do so throughout their lives.
Reiki's most distinctive feature is its apparent "instant" onset of healing power, which is also one of the most perplexing aspects for Westerners to grasp. Although we're not used to seeing things like this happen so quickly, it is common practice in the East to use spiritual empowerment to gain spiritual power. Even though Reiki has origins in Eastern spiritual traditions, that is not a religion, so that anyone can practice it regardless of personal beliefs. In addition, the ability to channel Reiki healing energy does not depend on a person's intellectual capacity or level of spiritual development, so people of all ages and backgrounds can learn to do so by undertaking a Reiki First Degree class and receiving the attunement. There are no prerequisites for understanding Reiki, making it a very accessible self-healing method and helping others.