The Jagan (邪眼, Literally meaning: Evil eye) is an additional eye that can be implanted that allows its user to amass various capabilities. It was used only by Hiei who received it through surgery by Shigure.
The Jagan is a third eye, placed in the middle of the user's forehead. It is the size of a normal eye, but the iris and pupil are thinner. Hiei's Jagan has a violet iris. It should be noted that not all demons with multiple eyes are considered Jaganshis, as several weaker demons in the series are shown with three or more eyes. Only those whose third eyes are implanted in such a manner are given the same abilities as Hiei and are known as Jaganshis.
Shigure the Osteopath is the one that conducts the surgery. Seemingly, a machine with a drill digs into the forehead of the patient, then implants the Jagan, via an incision that is precise to one seven hundredth of a millimeter. The procedure is extremely painful (Shigure must strap the patient down to prevent them from clawing out their own eyes) and taxing on the patient, so much that it made Hiei drop from an A-class to D-class.
Shigure asks for the patient's life story rather than money for payment, agreeing to operate only if their story holds his interest. Shigure seems to be interested in only tragic or extremely astonishing stories. If he's interested, he takes an important part of the story away from the patient. In Hiei's case, he could not inform his younger sister of their relationship.
Hiei, an A-class demon at the time, turned into a D-class upon the surgery. This was due to the Jagan needing so much energy to grow. However, as the user becomes more adept at using the Jagan, it grants them several mental abilities:
- Telepathy: Allows the user to communicate mentally with others.
- Telekinesis: Showed a limited ability to move objects with his mind.
- Mind Control: The Jagan, allows the user mind control over youkai and humans, provided their spiritiual power is low enough. It also allows him to cast illusions, transform people into his mind slaves, create false memories and erase them too.
- Mind Resistance: The eye also gives the user complete domination and control of his own mind, able to resist powerful mental attacks.
- Remote Viewing: The main skill of Jagan, is to enable the user to look vast distances, and can locate an object the size of a marble, miles away, regardless of location perfectly. It can see into houses, forests, and even caves with exact precision. This ability also allows the sharpening of his other senses, seeing how Hiei could hear a conversation between Yusuke and Yomi, from miles away.
- Heightened Senses: All senses when the wearer has the Jagan, increase to a supernatural level, Hiei could realize a minimum displacement of Yusuke's muscles, and thus predict that it would move to attack. This ability can see minimal movements, and predict the attacks of opponents even before they are executed. He could see the arm positions that Kuwabara and Kurama would make at Rock, Paper, Scissors, and also detect little whispers of offense of Kuwabara.
- Energy Manipulation: The Jagan also allows the user to perfectly understand his own energy. With Jagan, mastering techniques can be done several times faster than normal. This also stems to aiding Hiei in the manipulation of his Fist of the Mortal Flame to the point where, during the finals of the Dark Tournament in his match against Bui, Hiei became able to incinerate anything with a mere touch and project the flames.
- Demonic Fire Maipulation: Hiei's Jagan glows when he uses his Dark Flame techniques, implying the Jagan played a role in his mastering them (probably to psychically understand their properties and control them). The eye also allows him to enhance the strength of his technique, which normally wouldn't be possible, and grants him the ability of the Black Dragon Wave, as a Jaganshi.
- Raigo possessed a Jagan as well (though his seems to be more natural than artificial, considering how he can make it disappear). Raigo's mind control abilities seemed to be greater than Hiei's, with hypnotizing spirits surrounding the victim when he casted the spell, but he was unable to predict that Hiei would be resistant to his mind control.