"shakugan no shana" details an age-old conflict between those who inhabit the , a parallel universe to the human world. the crimson realm is populated by who are able to manipulate the , a fundamental power within any biological entity and functions as "fuel" for one's existence. denizens whose power stands out among their peers are known as , and lords that are even more powerful are known as . denizens who do not care about the balance between the crimson realm and the human world collect power of existence from humans to use for their own purposes. it is the duty of , humans who have formed contracts with a crimson lord, to maintain the two worlds' balance by killing any denizens disrupting it. denizens and flame haze fight with the use of powerful magic spells called , which are also known as unrestricted spells or unrestricted methods. one such spell is the , which creates a space where the crimson realm and the human world intermingle and all sorts of causalities, including time, are stopped for ordinary living beings.