Black Flash is a technique in the anime and manga series Jujutsu Kaisen. It is a distortion in space that occurs when cursed energy is applied within 0.000001 seconds of a physical hit. When a sorcerer is able to achieve this, it results in a damage multiplier, dealing 2.5 times the damage. The technique is considered to be one of the highest forms of cursed energy manipulation in the series.

Not all sorcerers are capable of using Black Flash, and it demands tremendous talent, fighting prowess, and in-depth knowledge of the management of cursed energy. It is a rare ability that only a handful of people have mastered over the years. So far, only a few users in Jujutsu Kaisen have been seen using Black Flash, including Yuji Itadori, Kento Nanami, and Nobara Kugisaki. Nanami is known to be one of the very best users of Black Flash in the series.

In summary, Black Flash is a powerful technique in Jujutsu Kaisen that results in a damage multiplier when cursed energy is applied within a minuscule amount of time after a physical hit. It is a rare ability that only a few characters in the series have mastered.