One of the greatest appeals of Jujutsu Kaisen is how densely rich its combat system is. There are several rules to battling with cursed energy, but with how intuitive they are, having a fair grasp of just a few allows fans to read into subtleties many other battle shonen simply aren’t concerned with delivering. One of the series’ most interesting concepts is the Black Flash, a jujutsu phenomenon that more often than not occurs by pure chance. In the final battles of Season 2, the Black Flash was used to great effect and ended up defining the highly acclaimed Shibuya Incident’s electric conclusion.
Source：https://www.cbr.com/jjk-black-flash-users/
