Incense

Incense (香) is a type of biotic, aromatic material, as well as the fragrant smoke produced when the material is burned.

It is used for various reasons, including aesthetic and therapeutic purposes, as well as meditative and ceremonial ones, which also mean that it plays a role in certain forms of magic.

Principles
A vessel which incense is burned in is known as a Censer (香炉).

World War III Arc
While undergoing Elizalina's treatment to remove the Body Crystal from her system, Takitsubo Rikou was connected to an oxygen mask which, instead of an oxygen tank, was connected to an incense made from dried and crushed plants.

Toaru Majutsu no Index SS: Agnese's Magic Side Work Experience
When returning to the United Kingdom to investigate leads connected to the Guild, Agnese Sanctis, Lucia and Angelene underwent a decontamination and purification process in a metal container, involving a special incense, to make sure that they did not bring any curses into the country.

A Necessarius magician tasked with observing the Agnese Forces wielded a censer and a cross, with Agnese noting the two as standard for an area-of-effect attack but not very flexible, guessing that he would usually be "dropped in" to crush a magic cabal on his own.

Magic God Othinus Arc
Spirit-reflecting incense was mentioned among examples of stories involving things within one's head being drawn into reality.

Kamisato Rescue Arc
The Kamisato Faction's ghost Goryou Maya made use of drones named Censers, which emitted imperceptible low frequency waves and aromas, to create an artificial haunted location to sustain her existence and exert corporeal influence, as well as maintaining an additional supporting incense in the form of her own scent.

Aleister Crowley Arc
During a vision of Aleister Crowley's past shown to Kamijou Touma in the Windowless Building on December 11th, incense was apparently being used during a magical experiment involving his wife Rose Edith Kelly.

Coronzon Arc
During the battle in London, Aleister Crowley noted how simplified incense is standard for constructing a ceremonial ground (mentioning oil, candle, stick, powder and mist), while using a windborne powder to spook the Female Knight's horse to get her out of harm's way. Incense was also mentioned as one of various mediums used to describe the soul, in reference to the problem concerning the disembodied Lilith Crowley. At least one member of the reproduced Golden Dawn wielded a censer.

Coronzon made use of a ceremonial sword and a metal plate with powder, burned for a camphor flame, to carry out a banishing ritual in the Queen Britannia's temple.

Christmas Day Arc
Incense was mentioned during Touma and St. Germain's battle with Anna Sprengel on Christmas Day, having been referenced on a sign in a jewel store touched by R&C Occultics, which had an offer to create a personal incense to add something extra to yoga sessions. St. Germain remarked on how one was supposed to rid themselves of worldly thoughts and possessions while doing it, though beginners might find it easier to focus on their breathing if the air was given an aroma or color - adding that using a guide meant only following rails laid out from them, so the act would lose meaning.