LucasHidemiKomori said: Erm... Where is Nano's winding key?
Personally, I assume she removed it when she went evil.
EDIT: Translated the artist's commentary, and this is confirmed. Well... kinda more like the removal turned her evil, not vice versa.
"In the classroom Yuuko: 'If the screw in Nano-chan's back were removed, her real self would show itself! For instance, she could, say, conquer the world!' Mio-chan: 'ARE YOU STUPID?!'"