Aki - Spirit of Words

The Spirit of Words/Kotodama The Spirit of Words, or the Kotodama, casts illusions. It is a high-level psychic device. The user activates it simply by announcing the names of the illusions that she wishes to appear. These illusions are so convincing that an opponent who believes that he has been bitten by a snake will actually suffer from a real wound. This is because the illusions that the Spirit of Words casts is able to trigger certain nerves in the human body which will cause pain. 
For example, when an illusion of snow is created, this will trigger the nerves that alert the body when there is a change in temperature, and the victim's body will begin to feel very cold, as if he/she were in a REAL snowstorm. It's highly likely that the victim will "freeze" to death if he doesn't realize that it's an illusion in time.
The illusions created are also visible only to the user or the victim - the others who are outside the field will not be able to see what is happening.

Aki normally doesn't utilize the Spirit of Words' full power. Already, in using a small percentage of its power, she is able to create such convincing illusions. Thus, when the Spirit of Words is being used to its full potential, the illusions are so powerful that the illusions actually become, in a way, real. Even if you know that they're illusions, they'll still hurt if they hit you. (The average illusions don't work that way.) 

Aki also has another weapon which was not shown in the anime. She has this thing coiled around her wrist that, likes like any ordinary ornamental bracelet, but when straightened, becomes stiff and can act much like a sword (or fencing foil) would. However, since it is smaller than a real sword, with a sharp point at the tip which is used to pierce enemies, it is much easier to carry. There is less chance of it dropping from her hand, as well, since half of it is still wrapped around her wrist to anchor it there while the first half is being used as a sword. Its cylindrical sharp also enables Aki to plunge it into other cylinderical shaped objects like the barrels of guns (or brooms which shoot out projectiles, as is seen in book 25 in the battle against Miruku and Kurumi). In the anime, this weapon was replaced with a fencing foil.