The two were confident that if they failed to keep their sense of self, then they would die. Two had actually had a very close call with this, it was why he had disappeared for a week. He had only barely managed to recall who he was in the sea of nothingness that Tranquility was.
Auras were truly unimaginable in power, at an unimaginable cost. As proven with Two's case, even the soul would be consumed. If there was an afterlife, the user of an aura who failed to keep their sense of self would never be able to join it.
Spirit magic could be considered a lesser version of auras. The two had realized that Incinerate was actually spirit magic.
Spirit magic was when emotions are used to activate and fuel a spell, instead of purely mana. It certainly is a shortcut to power, but it is far less stable and far more dangerous to both the caster and target than elemental mana.