This is weird... on the main page Nu doesn't show up on the image yet when I see it on the original source or view image on another window/tab, Nu shows up o_o
Looks like a trick with transparency. If you can't see the second character while viewing the image on this page, try one of these: If your browser has a console, run this in it:
Huzzah, now I have a way to check if an image has a white or transparent background without downloading it now that Danbooru doesn't turn it black in thumbnails.