Rainbow
The Rainbow is an uncommon tool-type martial soul in the Soul Land novels, notable for existing in a natural fusion of light and water, a built-in blend of elements that marks it as a powerful spirit.
Most martial souls in the Soul Land novels command a single nature; the Rainbow is described through the exception it embodies. It is a tool spirit whose form fuses light and water, existing from awakening in a state of element fusion that other spirit masters labor toward, and that built-in harmony of two natures is the source of its regard.
Within the setting's system a tool spirit shapes the abilities its spirit rings grant, so a soul that is itself a standing fusion of elements promises combinations a single-nature spirit cannot reach. The stories treat the Rainbow as a powerful and uncommon soul on that basis, an arc of merged light and water carried in a spirit master's body.
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