-The game was supposed to be divided into a trilogy of three games, later changed into three chapters compiled into one game
-There were four crystals owned by four nations: Lucis (based off of Tokyo, Japan), Accordo (based off of Venice, Italy), Tenebrae (combination medieval German/oriental theme), and Solheim (Arabian theme). A fifth nation, Niflheim, took over Solheim a long time ago, and eventually Tenebrae and Accordo too, quickly using up all their crystals' energy, which led to Lucis' crystal being the last active crystal in Eos, setting up the main conflict in the game. Niflheim itself was originally made up of a bunch of "non-crystal" nations, which were united a long time ago under one nation by the Aldercapt family.
-The first game (or chapter) started with the invasion of Insomnia by Niflheim (instead of the Kingsglaive movie)
-The invasion was orchestrated by Iedolas, the Emperor of Niflheim, and Clarus Amicitia, a cousin of King Regis, and father of Gladiolus and Iris Amicitia, although Clarus's role is hidden during the first game/chapter
-Glauca was introduced as a Lucis general related to Cor Leonis (twin brother?), and loyal to Clarus, shown working with Niflheim to help set up the invasion. The ”strongest" general in the Lucis army. He does not kill Regis, Clarus himself kills Regis at the end of the first game/chapter.
-Noctis met and fought Aranea for the first time in this game/chapter. She is a mercenary hired by Niflheim, and stops working for them when they stop paying her in the later games, pretty much exactly like in the final version.
-Ravus was the final boss of the first game/chapter. He and Stella Nox Fleuret were both from Tenebrae, and Ravus knew about the true intention of Niflheim to invade Lucis, while Stella did not. After several encounters throughout the first game/chapter with his hood on, he reveals himself as Stella's brother in the final boss fight. Although nominally a general of Niflheim, he was secretly working for Ardyn, and was specifically there to protect and capture Noctis under Ardyn's orders (during the first game/chapter, Ardyn's identity as Ravus's master is hidden). At the end of the boss fight, Ravus manages to escape from Noctis.
-Ardyn was portrayed as a silly and disinterested bureaucrat for most of the first game, kind of like how he is portrayed in the final version, in contrast to the other serious and calculating generals of Niflheim, with very few hints dropped in the first game/chapter that Ardyn is somehow the one pulling the strings behind the scenes
-The first game/chapter ended with Niflheim's invasion of Lucis being a success, and a new puppet government of Lucis being set up under Clarus, who agrees to share his crystal's energy with the rest of the world. Noctis and his gang escape the city and look for a safe haven to plot "revenge". Other characters also escape from the city, such as Cor, Iris, etc.