This recommendation is mainly tied around the 1st and 4th episodes of the Kuroshitsuji II specials. Nunnally in Wonderland basically sticks the Code Geass cast as characters in Alice in Wonderland. The two aforementioned episodes of the Kuroshitsuji II specials does exactly the same thing. Both of these specials are just fanciful stories where we get to see a familiar cast in a different light. (The other episodes of the Kuroshitsuji II special does this even more, but just not in a way that is as similar to Nunnally in Wonderland.)
Kuroshitsuji was intresting at the first 1-10 episodes. I started to watch it and it was pretty good!