Japanese

[marie curie]

if you want internal martial arts search for Chinese Internal Arts:

Qi Qong, Tai chi, Xing Yi, Pakua.

I know that "Chi" is the Chinese word for it (or qi in pin yin) so if there is a Japanese word in common use (Ki), then I'd think there were Japanese Arts involving it.

[Kajukenbopr]

I'll say that Aikido is an internal martial art from Japan.(though I dont know what the internal part of it is)

Supposedly jujitsu is an internal art also.(talking about energy manipulation)

I have no concrete knowledge of the internal arts of the Ninja, though they are supposed to have special meditations also.

Ki and Chi refer to the same thing - the universal form of energy that flows through everything and gives us life.