I know a master who only does Japanese empowerments at Reiki I and II, but when the students use the Symbols traditionally taught in Western Reiki, or meditate on the Symbols, they work. And this is without doing the over complex Western style attunment, which varies with virtually ever Master anyway.
The aim of the Symbols is to focus intent, as is the use of the kotodama, the vocal mantra version of the symbol. The Japanese form of Reiki is far simpler and not polluted with Western spiritualism.
So the KI is Reiki is the same however you come to it, so yes the Japanese techniques work!
If you like the meditations look up the Empowerment Reiju Ho. Done regularly, like Usui did to his students, before the symbols were deemed necessary and produced for the naval officers use, can open you as a channel more than any one-off attunment can.
John.
