Black Flash - 19 :

The key is to time your attack precisely at the end of a hit-stun on your opponent. How to Use Black Flash (Jujutsu Infinite)

You can often "chain" Black Flashes. After one lands, immediately re-engage with heavy attacks, as you may have a short window where another one is easier to pull off. 19 : Black Flash

Black Flash is a distortion in space created when cursed energy is applied to a physical hit within a trillionth of a second. It delivers 2.5x2.5 to the x-th power The key is to time your attack precisely

Some characters (like Yuji or Mahito) require you to be in a specific state—often activated by building up damage—before the Black Flash can occur. immediately re-engage with heavy attacks