Ki (氣; pronounced "Kee"), also known as "spiritual power", is the source of the power for every special abilities and superhuman technique. Martial artists are those people whom have learned to manipulate their ki to achieve such feats as increasing their physical capabilities and accelerate their healing.

Ki normally generates within the body and is limited primarily to internal vital functions. As such, it can not be projected directly from the body as raw energy. However, it can be channeled and transmitted through particular media. Many martial artists have also demonstrated that Ki can be channeled or transmitted through and/or into physical objects using certain techniques.