Because of wars the number of Spirits increases, this has left the Spirit World no longer able to handle it. Different types of departed spirits have different types of abilities and strength. The Human Martial Spirits are comparatively average on the whole, while the Beast Martial Spirits are more inclined towards agility and shrewdness. The Celestial and Demon Martial Spirits on the other hand, have the ability to use designated sorcery. Behind the surface, there is another type of Spirit that exceeds even the strongest departed Spirits, the God Martial Spirits, they do not need the support of Humans because their powers are more than just strong, as a result they usually exist on their own.
Not everyone has a Guardian Spirit, but if they do, it will help them in every way. Some spirits people are able to feel, others will feel a chill behind them. The only Spirits suited for battles are the Human Martial Spirits and Beast Martial Spirits. While the more unique ones are the Celestial Martial Spirits and Demon Martial Spirits.