Square Enix is banking on Final Fantasy nostalgia again for Final Fantasy Record Keeper. This smartphone game has a meta story where you help Deci, a student working under Dr. Mog, to enter paintings which contain memories of various Final Fantasy games. By entering say Final Fantasy VII, you can unlock characters from that game and bring them into other Final Fantasy games.
That’s how we end up with Kain from Final Fantasy IV and Snow from Final Fantasy XIII fighting Rufus or Dark Knight Cecil helping Terra destroy Magitek Armor.
Final Fantasy Record Keeper will be released on iOS and Android soon.