Kurama Clan's Kekkei Genkai

A rare trait of the Kurama Clan. Every few generations, a member will be born with an incredible talent for genjutsu. The clan member's prowess in that field is so absolute that even without proper training, their genjutsu is simply overwhelming. Furthermore, the genjutsu is so powerful that it causes the brain to believe anything that happens to the victim to the point where the genjutsu physically harms the victim's body in the same manner they envisioned. This fearsome ability allows the clan member to potentially kill their opponents with genjutsu. Such frightening power however is not without its drawbacks. The user is equally rarely able to control the full extent of their abilities, resulting in their subconscious regulating that power, leading to the creation of a second personality in control of that power. This personality proceeds to overtake the original, turning the individual into a monster that's a danger to everyone around them.