A few days ago I was playing through Azure Moon, and had Marianne and Sylvain reach B rank. In that support Sylvain says something about how people's smile shows you how they really are, if they are sincere of not.
The day after, Marianne reached A rank with Ashe; to my surprise, she quoted Sylvain and his thoughts. I re-checked these supports on youtube and confirmed that the dialogue does in fact change depending on Marianne/Sylvain rank.
This thing kind of blew me away! I wonder how many little changes like this one flew over my head during my playtime.