This light energy serves as a countermeasure to combat the the life-draining power of Akujiki, the demonic and soul eating sword. Because Akujiki feeds on Yin, the dark energy whose essence is comprised of humanity's negative emotions, its demonic hunger is suppressed by Yang.
For generations, the Oboro clan guarded the demonic sword. Eventually, the clan elders devised a ritual that would suppress the sword's hunger. The ritual ordained that the eldest heirs of the Oboro must engage in a duel to the death to decide who shall become the clan's leader. The victor would claim Akujiki and use the foul blade to kill his opponent, and the sacrificial offering would provide the sword with his Yang, which would ensure that the demon would remain dormant.
In this cruel suppression ritual, Hotsuma was forced to kill his brother, Moritsune. Although Hotsuma was initially hesitant to kill his brother, Moritsune was willing to be sacrificed and insisted that his life must be given to suppress the blade. Four years later, after the arrival of a mysterious golden palace and legions of Hellspawn in Tokyo, the gluttonous sword awakened, and Hotsuma was forced to satisfy its vile hunger. He used the blade to destroy the Hellspawn and the mad sorcerer, Hiruko Ubusuna.
- In Japanese spirituality, Yang is called Kon, which is the soul that gives life.