Acquiring My First Familiar Spirit!
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Spirits. Creatures made by the world itself. They're born in areas with high concentrations of Mana and Elemental Essence. They're made up of large quantities of Elemental Mana compressed into a living being.
It is said that Spirits are the pillars of the world, they're made of elements and even maintain the elements of the world by being many, they contain areas with a lot of mana together and don't let it fall into miasma either. They're the ones that protect the world that nobody knows about.
Belle herself was a spirit in a sense. She was a being made out of pure dream mana therefore, she could be cataloged as an artificially made spirit. I can see that something so hard to make would only come out of a Venerable.
I do remember that the original Belle could create Spirits herself, so perhaps she merely shaped this Belle using such a Unique Skill and her power as a Rank 10 Venerable to create a powerful dream being with her consciousness.