In my view, the discontinuance of this tag should not happen because it is useful for users who want to see Aya wearing outfits with such characteristics. By extension, in that sense its utility may be similar to the Kourindou Tengu costume. It can be interpeted as a broad "skin" that not only applies to a given character, but to any character wearing it.
Character skins tags exist for other series (e.g. Azur Lane) and they allow for a more specific search and indexing of matching posts, which is consistent with statements found in howto:tag (namely, "tagging an image with keywords which describe the content" and "tag the visual and factual elements in the image").
A small tag count might leave the general impression that it is not useful or worthy to be added to other posts, but for this tag in particular there are probably many untagged posts that match the definition. As the tag count widens, there is a higher chance that more users will be more appreciative towards it.
Should the BUR be rejected, I will embark on the task of expanding this tag with matching posts not for personal preference, but for the betterment of the database.