Naruto Curse Seal -

: Itachi had a similar but distinct seal. This was used to prevent his death from a then-terminal illness and brain damage he sustained. It allowed Itachi to survive and maintain a semblance of control over his body even after seemingly lethal injuries.

From a shinobi tactical perspective, the Cursed Seal is a "cheat code" with a subscription fee.

The Cursed Seal has distinct stages of transformation.

“Release Sasuke,” he said, his voice not his own—calm, lethal.

Here is a comprehensive guide to the Cursed Seal, covering its origins, mechanics, levels of power, and known users.

You could beat him, the seal whispered. You could save them. Not with the Fox’s rage… but with your own cunning. Your own speed. Take it.