A hotly debated question in the world of Reiki Practitioners is whether or not one needs to" "ask permission" before sending Distant Reiki Healing. Many feel we need to ask permission of the persons "higher self" or soul/spirit, but others object to this saying that there is an "unfairness" about it or it is unethical. That we are somehow bypassing their free will by going straight to their higher being. I'm on the fence about this, so I just say at some point during the process, "with their permission."
There are those who feel that before you perform an "in person" Reiki session on someone you need to verbally ask their permission also. If you perform Reiki sessions on the public and charge a fee for it, it is standard operating procedure to require your client to fill out a "permission to treat" or a release form. I personally feel that if they read and signed it, I have their permission, making it a moot point.
If you are sending someone Distant Reiki (also called Absentia Healing or Long Distance Reiki) and they did not ask for the energy to be sent to them (the request came in from a family member or friend), then yes, you need to energetically ask their permission. When sending the Reiki energy to someone under these circumstances, after you have gone through whatever procedures you were taught to use when sending Reiki and have stated their name, location and why you are sending Reiki to them, you can simply add that you are sending it with their permission and for their highest and greatest good.
My feeling about the debate is that Reiki, being spiritual energy and coming from the Divine (whatever the Divine means to you) asking permission from their higher self, spirit/soul whatever you want to call it, makes perfect sense. But as not everyone is in agreement on this issue either, best to just do what you personally feel is right.