Mithgol said:
I changed it to an artist tag.
Here's how to change a tag's type, from help:tags:
When tagging something, you can tell Danbooru that a tag is an artist tag by prefixing it with artist:. For example, tagging something artist:mark tree will tag a post with mark and tree. If the mark tag doesn't already exist, it'll be created with the tag type set to artist. You can also use art: as a shortcut for artist:.
If you would like to change the type of a tag to artist after it is already created, you can use the same artist: prefix to do so by editing the tags on any post that has it. You can also search for the tag and use the "edit" link next to it to change its type. Note that you are not allowed to change the type of a tag with more than 50 posts unless you are at or above the Builder level.
I'll add this information to howto:artist as well.