The user decrypts a genjutsu that has been applied onto them, and casts back a technique with identical effects onto the opponent. It's a form of illusion reversal, but in order to instantly read through a technique and cast it in return, the Sharingan's power is necessary. As a genjutsu is initially used to confuse the enemy, this technique, which sends it right back to its caster, deals a high amount of mental damage, more than anything else.