Alien is a valid tag cos Lum and Rei realy are aliens, even tho they don't realy look like traditional aliens like those in Star Wars and the like. BTW, I'm Freimgul the artist :D. Thank you for tagging everybody who worked on this.
@ Carbonian The point is alien girl is a visual tag, visual tags only can be used if you can see them in the gallery, that's the reason you can see lala tagged as demon girl, or c:lala f:alien_girl doesn't give any results, lala doesn't look like an alien so she isn't tagged as so (I asked that one to the mods) so the same should apply to lum.