Code Geass: Shikkoku no Renya

Set in the same official history as the Code Geass anime, this story unfolds in a different era. Renya, a 17-year-old boy with a mechanical left arm, favors shuriken as his weapons. Renya encounters C.C., a mysterious witch who appears perpetually young. She has come to Japan during the historical Edo era in search of a new partner for a covenant. At the same time, a mysterious man who strongly resembles Lelouch appears, though his intentions are unknown.