Spontaneous Combustion

The so-called unexplained phenomenon of human combustion.
It was the spell that Kokutou Azaka favored. However, it was closer to psychic power than magecraft. In terms of psychic power, it would be called Pyrokinesis.
Spontaneous Combustion is a method of attack that causes the target to self-combust, rather than immolating the target directly.
There are many theories which explain Spontaneous Combustion, Azaka’s Spontaneous Combustion can be explained by an amalgamation of the Charged Corpus Theory and the Electromagnetism Theory. The Charged Corpus Theory suggests that the human body produces electrical current during states of psychological arousal which causes Spontaneous Combustion, while the Electromagnetism Theory suggests that Spontaneous Combustion is a result of an increased release of electrons in the atmosphere.
All incantations used to activate Spontaneous Combustion were musical notes, since Azaka comprehended magecraft and combat through music.

Garden of sinners Pamphlet: Kara no Kyoukai Settings Glossary