Yin Yang

The Yin Yang Ways (陰陽道) is JAPAN's counterpart to magic, developed by Geppei (月餅, "Mooncake") around the early NC0700's. Much of its focus has to do with the sealing of Hell Holes and the suppression of onis. About a hundred years after the invention of the Yin Yang Ways, the study, research, and practice of Yin Yang became structuralized, developing into the Yin Yang Arts (陰陽術).

Unlike common magic, the Ying Yang Arts are all performed though paper mediums known as "rei". Those who uses rei to perform Yin Yang are known as Yin Yang Masters (陰陽師; "Diviners" in the Yandere translation of Sengoku Rance).

Rei
Rei are created by writing special characters/glyphs onto paper. Higher level reis typically have more characters of greater complexity. People with ugly calligraphy or a clouded mind tend to fail in making reis.

A rei can only be used by the person who created (wrote) it.

Shiki Rei / Shikigami
A shiki-rei, when used, turns into a shikigami to do the Yin Yang Master's bidding. Low level shikigamis usually look like origami (folded paper), although high level shikigamis may have a variety of appearances.

Many types of shikigami exist. Some are capable of attacking, while some are used as barriers to block attacks. Some are used to rely information across great distances, and some can be used for spying.

Depending on the strength of the Yin Yang Master, the number of shikigami they can command at once, as well as the abilities of the shikigami, can vary greatly.

Because shikigami are made out of paper (shiki-rei), they are extremely weak against water and fire.