Reiki, according to the USCCB's watchdogs of doctrine is neither scientific nor Christian, and therefore, inappropriate for Catholics.
I've had what amounted to a good back rub from a Reiki practitioner who donated her time to a theater.
I hadn't really heard much of it before, but when I asked her exactly what it was, beside massage, that she was doing, she was a little vague.
Well, a lot vague.
And I don't think it was deliberate obfuscation. It seemed likely to me at the time, that it was similar to a lot of peculiar spiritual practices, (EST, what I refer to as "Theatre Buddhism," etc.,) in that adepts don't want to tell neophytes too much at the beginning, so that they can rope them in with the sensible, practical side of something.
The Big Truths are the purview only of higher-ups.
It's one of the reason I was so against the RCIA programs attempt at secrecy and surprise, no, no, sponsors, don't tell our catechumens what's going to happen to them when we ask them to line up in the sanctuary and we all impose our hands on them, let it be this great mystery, for maximum effect!
What are we, Masons? Skull and Bones?
But as I said, it was a good back rub.
(Incidentally, I followed along in the ritual books at the Katholic Kranial Massage Ekstravaganza this year, rather than just trying to remember the prescribed language and gestures... even more creative than I suspected.)