It begins with a fight against Ifrit, which Noctis using Bahamut to circle the entire tower of Lucius, throwing down sword after sword. Ifrit blocks as much as he can, with Noctis taking Bahamut's chance to slam Ifrit with a critical blow. The Shiva Sisters (Gentiana is one of them) appear in unison and freeze Ifrit to the bone, sealing his fate with a kiss. She then tells Noctos to "Take back the light" in a language that sounded like someone talking in reverse, which is Archeon language.
When Noctis and his gang enter the main building of Lucius, they see all of those who have die from the journey hanging in chains above the main Chaos Crystal, which Ardyn sitting on the thrown. The image is truly disturbing, and all vanish into a puff of purple flame. Noctis then seriously engaged Ardyn outside the city in a flying battle (I am not joking) that is extremely similar to Neo VS Agent Smith from the third Matrix film. Ardryn has a copy of every Kings weapon that that Noctis has, only they are a red variation and his moveset is red instead of blue. They both fly, slam into one another using every single Armagear (spelling?) weapon, and continue to do battle unless Ardyn teases him how he was not even there to save Luna as she died. This enrages Noctis to go into a quicktime event where you literally throw every King weapon at Ardyn in sequence until he is virtually destroyed, telling Lucis he will "See him in the void."
He then explains the only way to truly kill him in where he come from, the Void, so Lucis steps inside to literally summon the ancient kIngs of Lucius to take his life (so that he can enter the void), when an army of Chaos Knights (with the huge sword) begin to form outside to kill his friends. They accept this sacrifice so they can meet Lucis in the Void. To make a long story short, they all attack Ardyn almost in the same manner, but he did not expect Lucis' friends to be there, overwhelming him. He seriously growly like a demon and sounds like Lucifer, with, Luna ironically appearing, grabbing him by the rist as a final move a deatomizing him. Ardyn, the First Crystal Bearer is destrotyed.
Another segment showing them having their life campire together and then it sadly switches to the grave of Noctis with a huge row of white flowers set all around the thrown. The next part is left open to interpretation, but it shows Noctis then sitting, happily married with Luna on the thrown as the TITLE screen for the first time ever literally changes, the logo of FFXV itself, with Noctis being drawn in beside Luna, who is the person who's head is lying down to the right in the logo. Noctics appears beside her in the logo, the game ends with the final picture Noctis choce to keep from Prompto to remember this adventure by. Literally, this is a FF where ever single person gives their life to save the world.