Curse

A Curse (呪詛) is a type of magic, cast with the wish to bring harm or misfortune on its target.

Principles
There are various methods which can be used to cast a curse. A common method is through Infection Magic which uses a person's blood, fingernail, hair or another body part to affect the person themselves. One of the most famous methods of applying this is through harming a doll made of straw, wax or corn, with part of the person attached to it. This traditional method has no real origin behind it, but has spread into various folklores and cultures, such as with Voodoo and Japan's Ushi no Koku Mairi. The and the  are two Egyptian-based means noted to be capable of applying curses. Similar to how everyday things used for cleaning and sterilization (such as water, salt and fire) can be used for purification, things that lead to pollution and decay can be used for curses. Two examples of such substances are mud and animal blood.

There are various curses which take undirected resentment or jealously and use magic to make it into an invisible arrowhead or bullet. Countless numbers of these travel around the earth all the time like high speed wireless internet connections.

As well as curses which are direct at specific people via various means, there are also many stories concerning items which bear a curse which falls upon those who come into possession of them. An example of this is that of a cursed jewel or precious metal which would kill each of its owners. Although pure gold is often used as a symbol of the incorruptible, it is also a popular choice for gathering curses, with its rarity capable of leading people away and becoming a source of jealousy and resentment. Mythological examples include the ring in Norse Mythology and the  in Greek Mythology.

A common concept in many cultures both eastern and western is the curvature of a curse. There are various methods which enable one to divert the path of a curse, such as having a straw doll take the target's place or escaping inside a magic circle drawn on the ground to divert the enemy's aim. Perhaps the most famous magic phrase, Aburakadabura (アブラカダブラ), is included in magic circles and charms, in order to perform a curse reversal (呪詛返し). When an enemy casts a curse, it will divert it or send it back at the enemy, as such it is widely known as a protective charm.

Aleister Crowley is a notable user of curses, who developed a technique which uses the curse reversal effect of Abracadabra and the curvature of curses to capture one of the many existing curses flying around and redirect it onto an enemy. During the destruction of the Golden Dawn, the magicians who survived being struck down by Aleister were said to bear a curse that took away their possibilities for success in life, dooming their choices to end in failure for the rest of their lives. This even included Aleister himself after he turned his own blade on himself in accordance with the rule he had set.

Three Stories Arc
The actions of Yamisaka Ouma were motivated by his desire to save a woman who had fallen victim to a curse.

Toaru Majutsu no Index SS: Necessarius Special Admission Test
Freadia Strikers makes use of a crystal radio to transmit a curse, based on folklore involving a cursed jewel or precious metal which kills its owners.

Toaru Majutsu no Index SS: Agnese's Magic Side Work Experience
During their Necessarius training in Barcelona, Agnese Sanctis, Lucia and Angelene had to perform a forensic cleanup of a magical battle site, including the careful disposal of a imitation corpse infected with a Voodoo curse. Shortly afterwards, having noticed signs of a magical cleanup in a restaurant, they investigated the circumstances surrounding the restaurant and its owner Nihili Padpois, who had moved to Spain from Haiti after the death of his wife, supposedly the result of a curse. The nuns eventually discovered that a curse-fearing priest carried out the cleanup to frame Padpois and get rid of him, given his previous contact with a curse. When dealing with the priest, Agnese tossed the remains of the cursed corpse over him after informing him about how pure gold, which the swords connected to his body were made of, could gather curses.

An aspect of the Ceremony of Ba Moun, which the nuns encountered in Frankfurt, where a demon will hunt and devour the caster if they don't provide the proper sacrifices, is described as a curse.

Isabella made use of curse-infested corpses during the attack on the Guild's base on. Later, when the nuns returned to the United Kingdom to investigate a lead on the Guild, they underwent a decontamination and purification process with a special incense to make sure they didn't bring any curses into the country.

Agitate Halation Arc
During his clash with Kumokawa Seria, Tsuchimikado Motoharu made use of the Ushi no Koku Mairi curse, applied through one of her eyeballs which he had plucked out.

Kamisato Rescue Arc
When Kamijou Touma, Misaka Mikoto, Karasuma Fran and Toyama Luca were investigating the core of the Anti-Art Attachment, Aleister Crowley made use of a curse reversal circle to direct a lethal curse onto Mikoto.

Processor Suit Arc
When Coronzon had to sever some of it's primary host's hair, it also severed a curse line built into it.

Coronzon Arc
It was noted during the events surrounding the Crowley's Hazard invasion of the United Kingdom and Touma's brief stay in the Tower of London that curses are utilized in the tower, with a curse scan of hair samples being used to verify the identity of individuals at the gates.

The reproduced Mathers' use of Belzébuth was also described as a curse.