just to be a dick: Ages ago, Alexander was designed by the author of the Enigma Codex as a haven for scientists and philosophers to research the mysteries of life. Two years after the start of the Seventh Umbral Era, a group of Au Ra, including Mide and Dayan, attempted to summon Alexander using the Enigma Codex. While Alexander appeared beneath the Thaliak River, a second version of it also arrived from the future. Illuminati Goblins aboard the future Alexander killed most of the researchers, and Alexander began to absorb aether from the surrounding land. When it attempted to draw Mide into itself, Dayan shoved her out of the way and was pulled in himself. As the last survivor, Mide executed their backup plan and conjured a barrier around Alexander. Though the Enigma Codex exploded, the future Alexander returned to its own time and the barrier kept the Alexander of the present from awakening. The Illuminati leader Quickthinx Allthoughts learned of Alexander's location in Thaliak River
in the Dravanian Hinterlands and repurposed it by infusing the structure's core, the Gordian Knot, with aether to serve as a primal.
Shortly after Ishgard joins the Eorzean Alliance, the Illuminati awaken Alexander. Cid nan Garlond and Y'shtola, the former knowing the Illuminati were the cause, witness Alexander partially emerge from the Thaliak River and enter stand-by mode while siphoning the area's aether. While Y'shtola seeks the aid of Matoya to contain Alexander from draining aether, the Garlond Ironworks secure the area around Alexander while investigating the apparent opening in its exposed hand with the assistance of Mide, who is after the Enigma Codex. After braving Alexander's defenses, the group shuts down the Gordian Knot. However, the Illuminati do not appear to be deterred, suggesting they have something up their sleeve
After Roundrox entrusts Mide with her "treasure", the final missing piece of the Enigma Codex, Alexander stirs again, with its second arm emerging from the lake. While Cid and Y'shtola leave to consult with Matoya, the Warrior of Light makes plans with Biggs and Wedge to breach this arm, known as "Midas", and shut down Alexander's second core, the Midian Knot. They are confronted by Quickthinx Allthoughts, who claims that Mide has been working with the Illuminati from the beginning.
When the group confronts Mide she admits that it is partially true. The initial attempted summoning of Alexander several years ago was not the work of the Goblins, but done by a group of Au Ra that she belonged to. The ritual went awry and the entire group besides herself was killed, and their leader—Mide's lover, Dayan—was absorbed by the primal's core. Mide told the Illuminati about Alexander, hoping that if they succeeded in summoning the primal, she could see Dayan again. She now regrets her actions and wants to stop the Illuminati's plans.
Illuminati has captured Roundrox, having learned that she can control the Enigma Codex, and by extension, Alexander. The Warrior of Light, Mide, Biggs and Wedge set off to breach Midas's defenses to shut down its core and rescue Roundrox. They get past the Illuminati's guardians, including a powerful robot known as Brute Justice, and disable the Midian Knot. When confronted by the Illuminati, they fail to rescue Roundrox and lose their piece of the Enigma Codex when Quickthinx accurately predicts seemingly random events. Once they escape Alexander, their Goblin allies claim they were only gone for a few minutes.
The group realizes Alexander has the power to manipulate time itself. Cid and Y'shtola rejoin them and reveal Alexander is reversing time to undo the damage the Warrior of Light's group caused, and restore the two disabled cores. Once this is finished, and with both the completed Enigma Codex and Roundrox in their possession, the Illuminati will have the power to rewrite history, creating a so-called perfect world that they control. They are joined by what appears to be Quickthinx's coeurl kitten, Shanoa, which indicates it wants to help them. Curiously, they observe Shanoa with Quickthinx at the same time.
Knowing that their only hope to shut down Alexander is to rescue Roundrox, Biggs disables the barrier around Alexander while Cid uses the Enterprise to deposit the Warrior of Light at Alexander's head. With the barrier down the giant awakens and fully rises from the river, but the barrier is restored before it can begin draining the land of aether. The band storms Alexander's control room and dispatches the Illuminati guards. Mide was hoping to see Dayan again, and Roundrox uses the Enigma Codex to travel three years back in time to when Mide and Dayan attempted to summon Alexander.
Their arrival messes up their summoning attempt, as the Illuminati shoot Mide and Dayan's companions. Shanoa jumps at their Goblin companion, who had been chronicling the events surrounding Alexander, and both she and his book tumble to the ground as Alexander returns to the present without them. The group takes Roundrox and escapes as Quickthinx Allthoughts arrives, but Mide stays. Realizing that Dayan was always meant to die, and that her efforts to see him again caused it, she wishes to remain with her lover's soul.
After regrouping, they return to Alexander's massive aethercyte core to shut it down, but it has grown so large that it is absorbing aether faster than they could destroy it; the only means of halting Alexander would be to use the Enigma Codex in the now heavily-guarded control room. Quickthinx returns and gloats that the future cannot be changed and the Illuminati will be victorious. Shanoa leaps at him and he drops his "futurebook"; the band realizes he has simply been reading from Backrix's tome, which was lost in the past, and that the future is not set in stone.
Quickthinx engages Alexander and halts time around the core before summoning Alexander Prime to destroy the Warrior of Light's group while they are frozen. Time unexpectedly restarts just before it fires, and Alexander Prime disappears into a time distortion. The Warrior of Light follows after it and during their battle, it sends several smaller units through time portals; the Warrior of Light follows and destroys them, which shuts down Quickthinx's temporal field and saves their own lives in the past.
Once Alexander Prime is destroyed, they return to the control room. When Roundrox attempts to use the Enigma Codex to shut down Alexander Quickthinx Allthoughts reveals that he, too, can access the Codex. Mide arrives and shoots him in the head. Roundrox disables the core, but Quickthinx revives and reactivates it, having replacing much of his body with machinery. Quickthinx commands Alexander to unleash its divine judgment on the ignorant and unworthy, but the Enigma Codex instead destroys Quickthinx before self-destructing.
As Alexander grinds to a halt, the monitors in the control room flicker to life, and Mide realizes that Dayan's soul really does survive within. Without the Codex to regulate the core, it begins absorbing aether at an accelerated rate; Mide throws herself into the core so that her soul can be with Dayan, and together they freeze Alexander forever within a single moment in time as their companions escape
Deep within the heart of Alexander, Mide is reunited with Dayan. He explains that Alexander foresaw all the infinite possible futures, and concluded that its own existence would inevitably bleed the land dry of aether, causing the end of the world. It intervened with history only once: to send a servant in the form of a clockwork coeurl to gently nudge history to a path that would ensure its own ending. Though they are now trapped within a single moment of time, Mide is happy to be with Dayan forever.
Shortly after Ishgard joins the Eorzean Alliance, the Illuminati awaken Alexander. Cid nan Garlond and Y'shtola, the former knowing the Illuminati were the cause, witness Alexander partially emerge from the Thaliak River and enter stand-by mode while siphoning the area's aether. While Y'shtola seeks the aid of Matoya to contain Alexander from draining aether, the Garlond Ironworks secure the area around Alexander while investigating the apparent opening in its exposed hand with the assistance of Mide, who is after the Enigma Codex. After braving Alexander's defenses, the group shuts down the Gordian Knot. However, the Illuminati do not appear to be deterred, suggesting they have something up their sleeve