When a genjutsu is used on them, the user quickly decrypts the genjutsu with their Sharingan to understand how it works. They then perform an identical genjutsu on their attacker, causing a "genjutsu reversal" (幻術返し, Genjutsu Gaeshi, English TV: Genjutsu Reflection, literally meaning: Illusion Technique Reversal). Since most genjutsu are used to confuse victims, this reversed genjutsu deals predominately mental damage. The effectiveness of the reversed genjutsu relies on how strong this technique's user is relative to their attacker and whether or not the attacker has any kekkei genkai of their own.
- Tō no Sho, page 274