The following dialogue sequences show what happened to Cid and Cidney's past, as well as what could have happened to Cid' son / Cidney's father.
Scene 1
Man in diner 1: After his son's accident, I never imagined the old man'd keep the place runnin'
Man in diner 2: Me neither. But he did, now Cindy's all grown up.
Man in diner 1: Yep. Hammerheads in good hands.
Here's the link -
Time [20:12]
Scene 2
Prompto: You reckon Cindy's taken?
Gladiolus: Don't think so.
Noctis: And you'd know.
Gladiolus: Not exactly hard to tell. A guard like hers doesn't come down easily.
Prompto: Even to a Casanova like you?
Gladiolus: Curious as I am to see, my priority's keeping his Highness safe.
Link to scene -
Time[16:56]
Scene 3
Noctis: Like a father to her?
Gladiolus: Ever since they got back, Cid's been the only one looking after her.
Ignis: Rather more than a middling mechanic can handle.
Prompto: All things considered I'd say she turned out ok.
Gladiolus: Like any girl, you just need to treat her right.
Prompto: Treat her wrong and Cid will stuff his wrench were the sun don't shine.
Ignis: Take care of the car and it will take care of us (Ignis totally missing the point here lol)
Noctis: Yeah.. the car
Link to scene -
Time [20:00]
From this, we can that something traumatic has happened to have caused Cid and Cindy to lose a loved one.
If you look closely at Cindy's eyes when she speaks, she looks kinda sad despite her cheerful demeanor.
And the sad look in her eyes doesn't stop with the beginning scenes of the game, even in this tech demo you can see her eyes tinged with sadness.
1:16
It's something I noticed awhile ago when I first saw her but couldn't explain why. This dialogue confirms that there's more going on with her character than what we've seen thus far.
I really do think that Square has taken the time to flesh out their characters in this game. We ain't seen nothing yet everyone. I'm starting to think that every character that will be introduced in the game will have a backstory to them.