Chapter 3, the flashback where Lelouch recruits Shirley. the poor girl has a case of Driven to Suicide and throws herself off a cliff. Lelouch uses his dragonslayer magic to save her and then tells her that her gift is real because she had lost her faith in her ability as a magus.
Chapter 9 where Marianne tells Kallen that she’s home.
Chapter 15 where Marianne calms Cornelia down while she’s having post-victory Heroic BSOD regarding the death of Estellise.