Necromancy

Necromancy is a type of magic that manipulates the dead, and is grouped alongside Hopping Zombie Spell, Hand of Glory, and Vetala Sorcery.

A user of Necromancy is called a Necromancer.

Etymology
The word "necromancy" is adapted from Late Latin necromantia, itself borrowed from post-Classical Greek νεκρομαντεία (nekromanteía), a compound of Ancient Greek νεκρός (nekrós), "dead body", and μαντεία (manteía), "prophecy or divination." As the name suggests, necromancy is the magic of manipulation of the dead for communication for the purpose of divination.

Principles
For uses of necromancy for divination, at least in the case of Isabella Theism's method of invoking a dead spirit to answer a question, it can only reveal lost information and cannot reveal information which can be found by methods available to the living.

Rosenthal-style Necromancy
With the use of Rosenthal-style Necromancy, rituals can be carried out on the bodies of the dead to allow them to "pass through the gates of Heaven". These rituals involves putting back the wandering "residual memory" of the corpse and closing their "spiritual circuit", in order to put them to rest. To do this, the necromancer makes use of a magic circle to reactivate the corpse and sends a false soul (偽りの魄) into the body in order to carry out the process.

If the "residual thoughts" (残留思念) are not controlled, they can take dangerous forms sometimes called ghosts. Residual memory can gather outside of the corpse, appearing in the form of a floating brain. If someone touches it, the memories of the deceased will flow into their mind.

The false soul used to possess the corpse, for the purpose of closing the spiritual circuit, is capable of operating the body it is possessing, such as when Esther Rosenthal's Huotou (禍斗) activated after she was interrupted before she could close Hitokawa Hasami's spiritual circuit and acted to defend it's master.

Kazakiri Hyouka Arc
It is referenced after Index sees Kazakiri Hyouka's leg regenerate completely after kicking Sherry Cromwell's golem down, and saving her.

Toaru Majutsu no Index SS: Agnese's Magic Side Work Experience
Necessarius necromancer Isabella Theism was involved in the events surrounding Agnese Sanctis, Angelene and Lucia's training and work for Necessarius, as well as the subsequent clash with the Guild, and used her necromancy during these events.

Necromancer Arc
Accelerator encounters a necromancer, Esther Rosenthal, during the events concerning the rogue Anti-Skill group DA, and Esther uses necromancy on the corpse of Hitokawa Hasami.

List of known Necromancers

 * Esther Rosenthal
 * Isabella Theism
 * Pantagruel