The entire story is one for Nunnally in general, or at least as long as she has the Mark Nemo, which she loses in Chapter 16. More specifically, though, is in the last act, when she delivers her "World of Cardboard" Speech as she, through SHEER FORCE OF WILL, stands back on her own two feet (which she never does in the original anime) AND opens her eyes once more. The fact that both her inability to walk and see were both rooted psychologically doesn't detract from this much.
Charles' whole coup d'etat. When Schneizel tries to use some bureaucratic nonsense to stop him, Charles just says "Screw you, I'm the absolute ruler now" and basically does what took most real-world dictators several years to pull off in one speech..