A special ore that contains a mythical power which is capable of draining a Demon's power. Hikarium ores can only go as far as to weaken a demon, but pure,refined Hikarium are capable of making a demon lose consciousness.
Since the discovery of Hikarium it is almost always used to counter Demons due to their abilities to weaken demons. Hikarium are sometimes used in weapons and armours to counter Demons, but these cannot be mass produced given how rare and expensive Hikarium is, not to mention Hikarium can lose their effects easily if an inexperienced blacksmith work on it.
Hikarium comes from Hikari, which means Light in Japanese.