User blog comment:Martialmaniac/Creating a page for Nanika/@comment-4828844-20161017062945/@comment-26871067-20161017064831

It was added as bonus material in volume 33! It's the first image in this set, and the text (translated) states "From the Dark Continent", with the "ai" catchphrase (so it's 100% Nanika and not Alluka, as if the face wasn't clear enough).