There are Strange Tales with compatible natures that can inherit the abilities of the originator through absorbing these relics.
As for why Mimiko and Kawazaru share compatibility.
It's probably because they both belong to aquatic Strange Tales.
In Japan, the kappa and the monkey have always been mortal enemies in folklore. Moreover, in some folk tales, their forms can transform into each other; for example, a kappa coming ashore could turn into a monkey, and a monkey entering the water could become a kappa.
Additionally, the legends of the kappa might inherently contain some "water monkey" hues from the Huaxia region.
Of course, such things were beyond Mimiko's understanding, she only knew that absorbing the relic was a good thing.
