Yin and Yang Release (
Official Version)
As chakra is created, the ratio between the physical and spiritual energy is dependent on the individual as defined by their personality, genetics and training. Some individuals generate chakra with more spiritual energy than physical whilst some are opposite. The ideal ninja would have a perfect balance between them. This is the same for the chakra that is constantly being produced within the body and the chakra that is deliberately generated. Most jutsu favour either physical or spiritual energy to some degree, depending on how they function, meaning that the energy ratio within the chakra needs to be changed when moulded to use the jutsu. The natural energy ratio of a person's chakra influences how easy or how difficult it is to use a jutsu. For example, Bunshin is a non-physical image so it uses spiritually-included chakra which is why Naruto, who's burdened with the Kyuubi's Yang chakra, struggled to learn it despite mastering Henge and Kawarimi.
It is only when the physical or spiritual energy composes at least 75% of the moulded chakra that it becomes Yin or Yang chakra. When there's more spiritual energy than physical energy, it is Yin chakra. When there's more physical energy than spiritual energy, it is Yang chakra.
Yin Release uses imagination and can bring form from nothingness e.g. genjutsu.
Yang Release governs vitality and can breathe life into form e.g. medical ninjutsu.
It's possible for this to be taken to extremes where the chakra is composed almost entirely of either physical or spiritual energy, causing it to become unstable and independently seek out its opposite form of energy to attain some balance. This is typically just a mistake made during training but some individuals have developed jutsu which use this as the main function e.g. Tayuya's Revolt of the Demon World.
Because chakra becomes unstable when the energies are so unbalanced, controlling such chakra requires special advanced training or unusual skill, hence why Yin and Yang Release jutsu either require very fine chakra control (genjutsu, medical jutsu), or the special training is a closely guarded clan secret (shadow jutsu, mind/body switch jutsu, body expansion jutsu).
Yin-Yang Release is an incredibly difficult art which uses Yin and Yang chakra together. It involves creating something from the user's imagination (Yin) and then giving it life (Yang). It requires the simultaneous use of both chakras and only the Sage of Six Paths was known for mastering it, resulting in him possessing the ability known as the "Creation of All Things".
