Aiki
Literally speaking, aiki is “union with ki (energy).” It is matching the rhythm and tempo of the opponent and being one with the enemy's mind and body. The purpose of this strategy was to understand and be aware of opponent intention and to counteract in an effective way.
The main stipulation for aiki is “opening the awareness (Munenmusô = free from impeding thoughts) and a correct application of breathing (Kokyû) connected to the voice (Kiai).”