Despite their rivalry on the battlefield, Astolfo and Mordred are pretty good friends with each other. When you encounter them, Astolfo will always see you as his master, and Mordred, when close enough to you, will either start seeing you as her father or brother (if you're a girl), or as her mother or sister (if you're a boy).

Astolfo: He is a kind and caring soul, wanting to help you find happiness, and will protect you from danger. Even when he's down, he'll find a way to still help people lighten up.

Mordred: Despite her sad and intense hatred for her father, Saber, who was originally Artoria Pendragon, she's actually a nice person to be around. A dangerous knight on the battlefield.