Well it's certainly not anime-related, unless it's something so abstract that it no longer resembles the original concept. I guess the main reason it was uploaded is that other works which may be (though they also streches the limits a bit) considered anime-like by this artist are already uploaded.
In any case, I dont think it's necessary to remove it. I think it's a pretty image, much better than much else I've seen on Danbooru (though that isn't the main point). While one irrelevant image encourages to upload another, images like this shouldn't be a problem unless they begin to invade Danbooru in massive numbers.
