Final Fantasy Type-0/WMG

The Missing Member of Class Zero Is Dead
Hence the graves in the latest trailer.

Said Missing Member was named Cater
They died because Four Is Death.
 * Jossed

The card based names are codenames
They don't seem to have any last names to speak of, even though their country seems to use them. And the theme naming is a little too on the nose.

The whole game was based on a Final Fantasy fanfic written by Walker from Durarara
Walker had always wanted to create a game with an Magical Academy setting with him as The Ace and his various acquaintances as team mates. Thus Dotachi became a archer with a perchance for grumbling, Celty became a white haired bishojo but kept her scythe, Shizuo is basically himself with his shades and streetposts replaced with a lance and scar respectively, and Shinra turned from Mad Scientist to mad king. Since Walker didn't know much about the cute Reira girl with glasses and huge breasts he turned her into a flutist. Izaya got his personality altered because otherwise he'll completely overshadow everyone else. Also, he made sure that the policeman with the red-scarf who gave them a ticket several times died a horrible death and ended up forgotten by everyone (though he got extra scenes later since he was actually kinda cool). Togusa and Erika are also in the game except they insisted on being the super secret bonus boss that can only be reached on the fifth playthru with no damage taken at any time, hence why no one has seen them yet.

The Diva that narrates the game is
That and she has the same voice actor as.

Jack is Demyx's Other
As it was stated above, the card based names are codenames. Jack's real name is Myde, Emyd or something that could be anagrammed into Demyx. One wonders why Demyx became so apathetic, though. As for his age, Leon is older than Squall, Rai, Fuu and Seifer are younger than their Final Fantasy VIII selves.