In One Piece series, there's this 'will' technique called Haki. Is this based on anything real, all three of them?
Haki appears to be similar in principle to common types of Qi (Chi) found in various other anime and manga series; which is based on the concept of "qi" (or "life-force") in Chinese philosophy.
The concept of Kenbunshoku Haki, known to Skypieans as Mantra, is loosely based on the style of thinking in Hinduism, which goes by the same name.
The original Japanese term is ki (pronounced the same as "key", written as 気). It can also be spelled chi or qi. The same term is used for a concept in martial arts.