Mandala

A Mandala (曼荼羅) is a spiritual and ritual symbol in Hinduism and Buddhism, representing the Universe. A Mandala uses complex patterns to make one think of the laws of the universe and the principles of the gods.

Principles
According to Itsuwa, it is an Eastern diagram of the natural laws of the universe. As shown by Itsuwa and her fellow Amakusa Christians, a Mandala diagram can be drawn on many objects, though likely only on flat surfaces such as tables and walls.

The Amakusa Christians utilized the principles of the Mandala as a form of illusory magic that only works on humans. The complex pattern of a Mandala normally makes one think of the laws of the universe and the principles of the gods, but if the patterns are rearranged it can send the desired image to the viewer's head.

Toaru Majutsu no Index SS: Necessarius Special Admission Test
During the events surrounding the Amakusas' admission test to Necessarius, Itsuwa drew a Mandala diagram on a table in order to create an illusion that Freadia Strikers' crystal radio component was at the center of it. After rescuing Itsuwa from Freadia, the Amakusa Christians used it on the walls of a drainage tunnel in order to make Freadia think that they have analyzed her crystal and have made up a spell to turn her own curse at her.

Itsuwa would later plan on using this on Emilie Fordia the same night, using a Mandala drawn on blank piece of paper. Itsuwa intended on sending an illusion of Emilie's number locked magic sword to make her lose control of it. The plan fell through after Freadia Striker decided to confront Emilie her own way.