When you go back, no matter how hard you try, the present won’t change.
-- Kazu (chapter 1)

Importance: In this line of dialogue, Kazu explains the first and most important rule of the café's time travel ability. If a character goes back in time and changes something, no matter how significant, the present will not change. However, as becomes evident throughout the novel, the characters are able to find certain leeway or loopholes in this rule.

Even that I can live with. It’s okay if nothing changes.
-- Fumiko (chapter 1)

Importance: After Fumiko learns that she cannot change the present by traveling to the past, she still desires to go to the past and redo her conversation with Goro. Her decision appears to be based in a desire to simply express her feelings and protestations during the break-up discussion. This fact reflects the emotional importance of such self-expression.

Because that woman…is a ghost.
-- Kazu (chapter 1)

Importance: In...