Is it a religion? Or against my religion?
While Reiki is spiritual in nature, it is not a religion. It has no dogma, and there is nothing you must believe in order to learn and use Reiki. In fact, Reiki is not dependent on belief at all and will work whether you believe in it or not. Because Reiki comes from God, many people find that using Reiki puts them more in touch with the experience of their religion rather than having only an intellectual concept of it.
Reiki is founded on the principals that is important to live and act in a way that promotes harmony with all creatures.