From time to time, I have been moved to discuss religion as it has been interwoven as a part of some Reiki practitioner's understanding of Reiki. My intent here is not to demean or criticize another person's religion, but, instead, to mention the trends that I see and to try to explain my understanding of Reiki and its possible religious roots. Usui, by all current accounts, was a practicing Buddhist. He was a member of a sect called Tendai, a tantric branch of Buddhism found in Japan. Some say that during his teen years he became a Shingon Buddhist [a more fundamentalist tantric sect] to annoy his parents. As did most other Japanese, he also practiced Shinto, the folk religion of Japan.
Recently, I have noticed many Reiki practitioners mentioning "angels", "saints", "mother Mary", "St. Germain, and the like. While they might be logical inclusions based on the stories by Takata that Usui was a practicing Christian, we now know that he was never a Christian of any kind, and that Takata "converted" Usui to try to make Reiki more palatable in the West. Hence, the only possible additions to Reiki would have their roots in Buddhist practice and historical figures. What I see is the inclusion of emotionally important figures from Christian history by well-meaning Reiki people who want to continue the good feelings and sense of personal connection with Reiki by using the important figures of their religious youth. The underlying belief seems to be that Reiki is God acting though them.
If there can be any justification of making Reiki more spiritual and tied to religion, it would have to be in the direction of Buddhism and Buddhist thought and characters [Tara, Kwan Yin, ascended masters, and the like]. This is not really possible, if one remembers that Usui himself did not see Reiki as a form or practice of religion, but one of healing based on a philosophy which he had discovered.