Magical Device Nemo

Magical Device Nemo, (魔導器ネモ madouki nemo) usually just called Nemo, is a character from the spin-off manga Nightmare of Nunnally and is one of the main characters. She first appears as a small white doll-like thing with a geass sigil on its face. Upon intiating her contract with Nunnally, she takes on the appearance of an albino Nunnally. She says that she is "an alternate manifestation of the girl Nunnally," and "the manifestation of darkness in Nunnally's heart." She is ferrously protective of Nunnally and will protect her from danger when possible. She can also create the knightmare frame Mark Nemo to use in battle, joining herself and Nunnally together in a her body. Nemo can normally only be "seen" by Nunnally, with the exception of Mao.

Geass
Nunnally and Nemo's geass allows them to "see the lines of the future", an ability that functions like precognition. It is similar to the geass used by Bismarck Waldstein, except that it is more effective because it tells the entire future instead of just one person's. A red geass sigil lights up in Nemo's left eye while it is activated. When combined with their the Mark Nemo, they are almost unstopable on the battle field, taking someone like Alice and her artificial geass "The Speed" to even contend. The geass apparently takes a large toll on Nunnally's body, because she is seen bedridden after long usage of the geass.