I was going to add in an alias koutaro_(pixiv160924)->koutaro because it seemed the pixiv # disambiguation was completely unnecessary. There are a lot of images tagged with Koutaro in right now (seems he's even artist for some game CG's) and the simpler form isn't really in use for anything at the moment. Wouldn't let me enter it because of the alias from nijiiro_zakura already there, so I decided to bring it up here. I'm against adding in Pixiv numbers to tags unless it's absolutely necessary (I think there are only a few very rare circumstances when they would). If there is a link to the Pixiv profile in the artist wiki entry, then the Pixiv number is known already and doesn't need to be in the tag.
Updated by albert