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First of all, my character is a Sannin. Thereby he wanders, and is quite often outside of the Amegakure and away from the rain.
Secondly, Shukaku has the ability to convert all types of earth into sand. By this logic, he should be able to convert mud into sand, which means that during times of rain, he would continuously convert the mud back into sand.
Furthermore, if sand is indeed a chakra nature, which at this point there is nothing that proves it isn't, it would be a mixture of wind and earth. This is not only logical, but would fill in the missing nature in this image: Chakra Natures
In the image: Earth + Water = Wood, Earth + Lightning = Explosion, Earth + Wind = Question Mark (unknown).
Earth is strong against water, and neither earth nor wind are weak against water.
Additionally, both my character and the Shukaku possess wind chakra natures.

If neither of them are weak to water, and one of them is strong against water, surely their combination would not be weak against water. Not to mention the fact that Fire isn't included at all, which is the nature that is weak to water. Besides, this does not disprove my continuous conversion argument. And the user does not need to have Earth as one of his/her affinities, since the Shukaku grants sand manipulation to whomever its Jinchuuriki is. Gaara is a prime example, whose only affinity is wind. Also the Jinchuuriki from Sunagakure died in Amegakure. There was no time to send a message to Sunagakure and wait for someone from that village to come, while Amegakure is being destroyed.

Ryan, he actually has a point, and Aiko said if you pick a demon that isn't from your home town, you can just ask her. Not to mention he isn't really a villain of any sort. I shall have Aiko take a look at this.

What part of my explanation didn't make any sense?