It's very simple: let's make the player experience action anytime these relationships are illustrated, especially if the original game mentioned them in passing. Example: Lino & Flare's reunion can be an actual gameplay event, with the need to fight to reunite them. Remember, this is a videogame. And videogames can be used as a medium to tell a story (thanks Murayama and Ron Gilbert!) but you have to tell this story using the medium. It's not a movie, it's a playable thing. The story is told through gameplay. So any kind of emotional link between characters is fostered through gameplay.
Honestly, I was moved when Nanami died, not only because of the dialogues she had, but because we saved each other's ass in front of so many dangers. Valeria is awesome not only because of her statements in favour of elves, but because I was there when she actually put these statements in action through so many uses of her falcon rune. The best thing about killing Luca Blight is not what he says when he dies, but the fact that you actually get to kick his ass. Your relationship to Teo is heartbraking because you actually press the button that will trigger a Special Attack on the face of your father. So you will learn to love all of S4's characters by playing with them.