Final Fantasy XV is almost its own thing at this point. It has more side projects and spinoffs than many AAA franchises just a year into its life cycle, and if I know Square, they aren't stopping anytime soon.
They aren't stopping today either, as King's Knight: Wrath of the Dark Dragon just arrived worldwide on iOS and Android. As a recap this is a free-to-play re-imagining of the original 1986 NES game King's Knight, but is somehow jammed into the Final Fantasy XV universe.
It's neat that they were able to bring a relatively forgotten game back into the fray, but the original is...a not so great shoot 'em up that was disguised as an RPG. It also had a terribly amazing conceit in that you need to beat the game with all four characters without dying to access the last stage/ending. If nothing about this mobile version interests you, it's worth learning about the NES edition.