According to official website, a spin-off OVA of Code Geass titled Nunnally in Wonderland was announced.

The said OVA is scheduled to released  this year on Blu-ray Disc and DVD. Discs include a 40-page picture book that recounts the same story as the anime.

Synopsis
In the all-new story, Lelouch makes the ultimate use of his Geass power for his little sister Nunnally, who loves Alice in Wonderland. [MAL]

[Source]