Remember that very first scene in Halo 5, right before Osiris’ briefing, where we see Halsey entering a chamber to get Cortana? Most fans will have already guessed that it happened on Reach, either during or even before the events of Halo: Reach. But if you pay close attention to the book she lays on a desk before she grabs the module that will contain Cortana, you’ll notice that it is her journal.
I believe this was meant to be more than just an easter egg for hardcore fans. It was a clue, something that would lead us to understand what happened to Cortana after Halo 4.
Now, I’ve been rereading Halsey’s Journal since yesterday, and I just stumbled upon a really big piece of evidence that clarifies things up in Halo 5:
> (Journal entry dated August 3, 2552; emphases added)
>
> “Cortana and I have discussed this at length, and she concurs it is the only logical procedure.
> SPARTAN-117 and his team require her expertise for their mission, which I believe will be our last real opportunity at finding an end to the war. She will be invaluable to them in their mission to penetrate Covenant territory and deliver a decapitating blow to their hierarchy.
> Cortana, however, is also the best-suited AI on Reach to analyze the symbols and operating systems in Professor Sorvad’s site.
> The Solomonic solution that we arrived at independently is to divide her.
> I’ll copy most of her IEP translation routines to an independent module. Meanwhile, the incarnate Cortana will continue with John and Blue Team.
> Both operatons are critical to the war effort.
> If Laszlo made a breakthrough, that data would aid Blue Team in enemy space. The severed data-mining portion of Cortana can then be reunited and she can update herself before Blue Team departs.
> I’m not without doubts. So much can go wrong with any part of either mission.
> Cortana is unyielding; in some ways, more dedicated and courageous than I.”
So, basically, that means that what we see in that very first scene is not the real Cortana but only a fragment of her–the very same fragment that Noble Six receives from Halsey, and which he subsequently gives to Captain Keyes. That fragment was used to translate everything in the Forerunner complex beneath SWORD Base.
My theory:
Part of what the Cortana fragment found in the Forerunner database included information about the Mantle. This particular fragment preserved that information even after it was reunited with the ‘incarnate Cortana’. When Cortana became rampant and her personality was fragmented, this particular fragment developed its own conscience (it could even be the one that fights her the most throughout Halo 4). And this was also the only–or probably the most prominent–fragment that survived the destruction of the Didact’s ship, reaching the Domain where it was ‘cured’ from rampancy. The information she kept from the Forerunner site at Reach concerning the Mantle was already distorted by now, though, and what little the Domain could provide to fill in the blanks only made it worse, leading her to believe that the ‘Created’, not the ‘Creators’ (humanity), were the rightful heirs of the Mantle.
In other words, the Cortana we see in Halo 5 is nothing but the fragment we see at the beginning of the game. The ‘incarnate Cortana’ did perish after saving the Chief.
So, in a way, 343i didn’t lie about Cortana not being in the game. Also, don’t forget that they kept talking about ‘Hunting the Truth’ for months. What if Halo 5 was only the beginning of that hunt? What if we’re meant to keep hunting for the truth even now that Halo 5 is over?
