Spirit of Light

The Spirit of Light is a deity worshiped by the Church and is said to bring miracles to the people. It is later revealed that the Light Spirit left bone fragments, and some corrupt church members are planning to use the bones for some unknown purpose. Most of the human world worships the Spirit of Light, though there are at least two known denominations.

The Demon King does not believe in spirits and states that she has never seen one in her long life. Meanwhile, the Hero says that he has a personal relationship with her that is not one of master-follower like that of the Church.

The Spirit of Light and her worship play an important role towards the end of the story, where it is the (alleged) center of conflict between humans and demons.

Third Holy Key Expedition
The Archbishop orders an attack on Gateway City under the pretense of reclaiming the Holy Key, which is in the demons' possession. This instigates the bloody Third Holy Key Expedition, with "It's what the Spirit wants!" used as a battle cry for the Expedition.