Tuning (調律 Chōritsu) is a spell that dispels the Distortion caused by the battles of Flame Haze and Denizens. The Tuning was used by a Tuner along with a human who was born and raised in the area that needed to be tuned.
Background
However, it is revealed during the events leading to the creation of the paradise Xanadu that Tuning a Distortion does not remove it, and should the Tuning be undone with spells such as the Anti-Seal the Distortions can be felt once again, Yoshida Kazumi who had become aware of the flow of the Power of Existence could feel something not being "right" when she took part in the process of activating the Anti-Seal with Lamies.