"Code Geass: Nunnally in Wonderland" is a special OVA episode that reimagines the characters of "Code Geass: Lelouch of the Rebellion" in a whimsical, alternate universe inspired by Lewis Carroll's "Alice's Adventures in Wonderland." The story begins with Nunnally vi Britannia, the younger sister of Lelouch Lamperouge, reading the classic tale to her friends. As she reads, the characters around her, including Lelouch, Suzaku Kururugi, Kallen Stadtfeld, and others, are drawn into a dreamlike version of the story, assuming roles that parallel their personalities and relationships from the main series.

In this fantastical setting, Nunnally takes on the role of Alice, who embarks on a journey through Wonderland to find her brother, Lelouch, who has been cast as the White Rabbit. Along the way, she encounters familiar faces in new guises: Suzaku becomes the Cheshire Cat, Kallen transforms into the Queen of Hearts, and C.C. appears as the enigmatic Caterpillar. Each character retains their core traits, but their interactions are infused with the absurdity and charm of Carroll's world.

The narrative unfolds as Nunnally navigates the surreal landscape, encountering bizarre challenges and whimsical logic. The Queen of Hearts, portrayed by Kallen, demands obedience and threatens to behead those who defy her, while Suzaku's Cheshire Cat offers cryptic advice and disappears at will. Lelouch, as the White Rabbit, is perpetually in a hurry, reflecting his strategic and driven nature from the main series. The story culminates in a playful yet heartfelt resolution, emphasizing the bond between Nunnally and Lelouch, even in this fantastical context.

The OVA maintains a lighthearted tone, contrasting with the darker themes of the original series, and serves as a self-contained, comedic diversion for fans. It cleverly integrates the personalities and dynamics of the "Code Geass" cast into the framework of "Alice in Wonderland," creating a unique crossover that celebrates both the source material and the beloved characters of the franchise.