Black Lightning is the highest level of Lightning Release.

To master lightning nature transformation, one must learn to vibrate their chakra at the highest speed and volume to create as much lightning chakra as possible in an instant. Black Lightning is born from refining this process to the absolute limit, increasing the frequency and intensity of the chakra vibrations to the maximum level possible. Once it reaches that peak, the chakra transforms even further and turns pitch black.

In this state, lightning chakra is closer to the true lightning of nature. It is capable of leaving flash burns and permanent nerve damage in its victim rather than temporary paralysis and pain, moving at speeds surpassing ordinary lightning jutsu and can even produce thunder claps.

Shinobi with exceptionally powerful chakra have been known to unconsciously create Black Lightning when performing Lightning Release but this is an incredibly rare phenomenom which may only happen once in their lifetime.

The art itself is a rare type of ninjutsu taught exclusively in Kumogakure but very few ever have the talent to learn it. The Third Raikage, who utilized this jutsu himself, started a tradition during his regime for the most promising students of each generation to be given the chance to learn Black Lightning. Those who succeed would be given the right to bear a lightning kanji tattoo to mark their mastery as a symbol of respect.

It is a testament to the difficulty of Black Lightning that only Darui was able to master it after years of training from childhood.

This type of nature transformation is not unique to lightning chakra and can be applied to any of the five primary chakra natures. However the only proven example is the black flame of Amaterasu which is said to burn anything and can only be extinguished by the wielder’s will. While this jutsu is tied to the Uchiha Clan’s kekkei genkai, it is technically possible to recreate it independently though it would differ from the original in how it is executed and controlled without a doujutsu.

Whether there is anyone capable of performing such a feat is another story.