Latter half of Chapter 6. It brings uncomfortable flashbacks from A's, when it's not being terrifying.
Chapter 15 has Negi spill his side of the story to Lindy. It's jarring hearing such a strong character break down like that. Though that says nothing compared to Asuna's reunion with him.
In Chapter 25, Lindy is forced to watch her son get attacked by an unknown source. She flashes back to the day her husband dies and faints.
