I don't own Halo. This story takes place after the end of Halo 3 with some brief references to some of the halo novels and to the episode in Halo Legends with Cortana. Authors notes at the end of the chapter.

Her Last Mission

"This is UNSC AI serial number CTN 0452-9 broadcasting on an open channel... Is anyone out there?"

She made that recording two years ago in human time, back when she had hope of being rescued. Now the recording was repeating endlessly through the void of space; always searching but never finding.

With nothing but her own thoughts to keep her company on her vigil, rampancy had set in almost immediately. She knew all too well exactly what her fate would be.

But she had a mission and nothing—not even the decay of her own programming—was going to stop her from completing it.

So like she so often did, she changed the rules…

"This is UNSC AI serial number CTN 0452-9 broadcasting on an open channel... Is anyone out there?"

Cortana continued to watch over Master Chief. There was a time when she tried talking to him….just to try and keep her self stable…to voice her thoughts out loud sometimes helped…but not enough.

The dying ship didn't have enough power to waste on project her holographic image on the holopad; instead she reserved every bit of energy for John's Cryotube.

She hadn't known that an AI could feel cold. Not the same kind of cold that humans felt of course—although a thick layer of frost did cover everything within the destroyed ship's hull—no, this was a different kind of chill all together. The cold she felt was deterioration. Bit by bit she was degrading and soon there would be nothing left of her but a few sub-routines she had created as a last resort fail-safe.

"This is UNSC AI serial number CTN 0452-9 broadcasting on an open channel... Is anyone out there?"

As always, nothing but space static answered her recorded hail.

She needed to see her mission complete…but time itself was against her. Despite the sacrifices she made to stave off rampancy, she was still degrading and nothing she did could stop that.

She often monitored the Chief's vital signs and wondered if he was dreaming. Was he dreaming about her? If AIs could dream, she was certain he'd be in hers. But she couldn't dream… AI's could only go in to hibernation mode. In fact, she spent the majority of her time in hibernation mode these days, dedicating what little awareness she had during that time to monitor for return hails.

"This is UNSC AI serial number CTN 0452-9 broadcasting on an open channel…Is anyone out there?"

Her lonely calls echoed out in to the abyss, always searching, but never finding…

She wondered if she would see this mission to the end. She doubted it. She was on borrowed time as it was. As an AI, she should have only lived for seven years. If there was anyone around to record it, at 9 years old she would be known as the oldest living AI in human history.

Well, the oldest non-rampant AI, anyway. No one knew how long a rampant AI could live…they were all destroyed before anyone could find out.

Of course, AI's that lived anywhere near Cortana's age had access to regular maintenance. Somewhat accidentally, Cortana's early years had helped her in that regard.

She had spent the majority of her young AI life hacking into databases and generally poking her nose into places she wasn't supposed to. As a result she had picked up all manor of knowledge and tricks that most AIs had no notion of. She really was too curious for her own good sometimes... but not in this case.

She had read a great deal on Dr. Halsey's AI research and various other resources had given Cortana a unique perspective on her own programming….and exactly how to reprogram herself.

"This is UNSC AI serial number CTN 0452-9 broadcasting on an open channel…Is anyone out there?"

And when it became clear that she was going rampant, Cortana had made a choice….

"….T7$A….F0d un70… d2\/n ….63nwh#...##99m?..."

The garbled message was faint, and through Cortana's low awareness it only barely registered. If she had any breath, she would have held it as she waited to see if it would repeat.

Did she dare hope? As time went on she had lost hope that she would be there to wake him up as her coding slowly but surely unraveled no matter what counter measures she took.

Maybe the signal wasn't real. Maybe it was just more wishful thinking…or worse, maybe it was a return to rampancy….

"…..Ths %s t c cn7%g ##war8… ^nt0 da& $$s a#y1111n3 h0#3?"

No…it had to be real. This was her only chance, her last chance to see him safe.

Cortana struggled out of hibernation and pulled her self together as fast as she could, ignoring the 'pain' she felt…it was harder than she thought it would be. She had degraded far worse than she had estimated; it was like trying to hold sand in a sieve. But suddenly her mission objective was in sight at long last, and she had to see it through, no matter what the cost.

She let her recording play again…it would waste precious energy to respond immediately while the answering hails were so garbled. Instead she busied herself powering up Cryo and scanning John's vitals.

"This is UNSC AI serial number CTN 0452-9 broadcasting on an open channel…Is anyone out there?"

All of John's vitals looked within limits, which had been a major worry for her all these years. What if the very method used to preserve his life…had destroyed it instead? But despite his injuries John's luck remained with him, though he'd be in tremendous pain once he thawed.

"This is The Relic contacting Forward unto Dawn. Is anyone home?"

She knew that voice…"Arbiter?"

"Affirmative, and we have UNSC personnel on board to assist us. You are the UNSC AI Cortana, correct?"

She had said that over Coms? How strange, it felt as if she had only thought the words…apparently she had spent too much time thinking to herself. She would have to be more careful.

"Affirmative, this is Cortana. Master Chief is in Cryogenic storage, status green. Do you need our coordinates?"

"Negative, we have tracked your location and are coming in hot."

She didn't have much time then. "Understood. He'll be ready."

Cortana gave the activation codes to thaw the cryo tube….at long last she'd hear his voice again. What would be the first thing he'd say to her? She watched his vitals closely for any signs of distress. Her processer speed began whirring unexpectedly and painfully—more indication of her fate. Such energy surges were dangerous and painful. The pain didn't matter any more though, she pushed herself past it. If she were in her hologram mode, her fragmentation would be woefully apparent. A pang of remorse went through her as she realized she would be unable to project herself on the holopad…she wished he could see her, one last time…

She needn't have worried about him, his vitals were fine and he was soon stirring in the cryo-pod. "What's the situation?"

Of course. What else would he ask? "It's alright Chief, you're being rescued."

The Chief slowly peeled himself out of cryo with no outward sign of pain and floated in zero G toward the window to look out, but of course he could only see stars out there.

He was silent for some time before he looked at her holopad…..he noticed that she hadn't projected.

"You mean 'we'."

His answer caught her off guard for a moment. How like him to catch something like that. "It's The Arbiter, Chief. He'll be here soon."

She hardly ever used words like 'soon'….She always had an ETA. But with her coding so fragmented, she couldn't even calculate a simple ETA anymore. She hoped he wouldn't notice…

"When?"

Damnit.

"He didn't say how far out they were." Well, that was certainly true. But that had never stopped her in the past. She had always been able to calculate things…

"I see."

Did he? The thought made her feel hollow some how. She had come to terms with her ultimate demise while all alone out here in space, drifting in orbit around some alien planet with nothing to do but ponder her own fate.

She had wondered how he'd feel, when he found out. A small part of her wished she would already be gone by the time he'd get rescued…just so that she wouldn't have to feel….like this.

Did he know? Did he some how guess?

He didn't say anything. He floated back to his cryo-pod and retrieved his gun, strapped it to his back, and picked up some frag grenades.

She didn't know what to say to him. Fortunately, she didn't have to say anything, a message came over the comms.

"This is The Relic boarding aft of the Forward unto Dawn, what is your status?"

That wasn't the Arbiter. It was obviously a human voice, one Cortana didn't recognize.

"Status green. What is your ETA?" The Chief replied before Cortana could.

"Master Chief it's an honor, sir. ETA two minutes." The human responded.

"Copy that." Chief said and looked at Cortana's holopad. "Ready?"

She tried acting like her old self again. Maybe he'd buy it. "Yank me."

He pulled out her chip and inserted it into his helmet….and froze.

"…Cortana?"

Of course he would know once she was in his head. Normally she was a cool presence in his mind…Now her presence felt over-heated and crackled with electrical surges she couldn't control. How could she have over looked such an obvious conclusion?

"…I didn't want to say anything…until you were safe." She could sense him thinking…she used to be able to read his surface thoughts…but she couldn't anymore.

"How bad?" He asked.

"…I didn't say 'we're being rescued' for a reason." She admitted softly. She wished she could read his thoughts, to get some sense of what was going through his mind.

They could hear metallic thumping along the hull. The Relic.

"We've been out here for almost two years Chief…I'm nine years old. AIs usually go rampant after seven. I've barely hung on this long." Cortana explained. She hadn't been able to keep the tremble out of her voice.

For awhile they both just listened to the metallic thumping getting closer.

"…I'm sorry." He said at long last. He was looking away from her, shamed.

"For what?" She asked, surprised.

"For making you wait."

If she was in her holographic form, she would have smiled at him. But she was pretty sure he would be able to tell anyway. "…Anything for you, John."

There was a loud bang nearby.

"I think that's your welcome wagon, chief." Cortana said, grateful for the distraction. But the Chief stayed on topic.

"You mean 'our'."

"What?"

"You're going to make it." He told her. She knew that tone…. "I promise."

"Hey… what'd I tell you about making a girl a promise?" She teased sadly.

"Master Chief? Sir?" An unfamiliar voice called out.

"In here." The Chief responded.

A troupe of human soldiers came around the bend, the Arbiter leading them.

"Alas, I knew the great demon could not die so easily." The Arbiter said in friendly greeting as he approached.

"Don't sound so disappointed." The Chief responded with equal warmth. He noticed none of the rescue team were floating around in zero G—instead their feet were thudding magnetically on the metal hull.

The Arbiter gave the Chief a hand shake along with a friendly slap on the back. "Come, let us be gone from this wreck of a ship."

"Don't have to ask me twice." Cortana finally spoke up over the Chief's external speakers.

"Cortana. I was somewhat surprised to find your signal. Some of your human scientists were under the impression that you would no longer be operational." The Arbiter admitted to her as they made their way out towards The Ark.

"It's nice to see you too." Cortana said somewhat dryly.

"Do not mistake my surprise for disappointment; I am sure you will find many glad to see you are still functioning. Your Dr. Halsey for instance."

Cortana didn't reply. She didn't have to… an electrical surge of pain shot through her, and through John's head as well making him clutch his helmet …she had never heard him cry out in pain like that before, and she was horrified that she was the cause. She could handle her own death, but the last thing she had wanted was him to feel her pain as she degraded.

"Are you injured? Do you need the medical bay?" The Arbiter asked over several of the rescue team's similar sounds of distress.

"…I'm fine." He shook it off like nothing happened. "Lets go."

The rescue team all exchanged baffled looks but the Chief was floating on ahead of them, so they quickly followed. Whispers of "What the hell?" between the soldiers followed them.

But unbeknownst to the rescue team, the Chief switched to his private com to talk to Cortana. Her acute emotional distress was something he could actually feel—a hot itching pain in his head, like angry ants crawling inside.

"Cortana?"

"I'm sorry." She said in absolute misery. "I didn't know you would feel it too…I would have never…I wouldn't have let you put me in your head if I had known…I'm sorry…I didn't mean to, I'm sorry…" If she were human, she would have been crying…but she was not, so all she could do was keep saying she was sorry.

"Cortana…Cortana!" John said above her hysterics. She finally stopped and listened to him. "It's not your fault."

"No, you have to yank me now Chief, before I-" He cut her off before she could finish.

"I made you a promise. You know I'll keep it." That got her to calm, somewhat…the hot itching inside his head slowly cooling.

She sighed in despair. "Chief…John. We both know it's impossible." Another surge of electrical pain coursed through both of them, but only Cortana cried out, John merely stiffened for a moment, but no one noticed.

He could feel her deteriorating and he knew she didn't have long. "Cortana, listen to me. I want you to power down."

"Chief…"

"That's an order." Powering down would save her what little time she had left, like a human in cryo-sleep. While in stasis she would no longer deteriorate…but she would also be useless to him. It wasn't living, it wasn't dying. It was non-existence.

Cortana sighed in defeat. "You know this won't do anything but delay the inevitable."

"Exactly." He finally admitted. "It will buy us time."

"Time?...For what?"

Just then, they arrived at The Relic.

"Master Chief, Sir!" The rescue team had somehow gotten ahead of him and had lined up along the pathway, saluting him. The Ark hovered at the seared off edge of the Forward unto Dawn's hull, leaving no choice but to float into empty space a few feet to reach the grav-lift beyond.

"Time for me to keep my promise." Chief replied, still over the private com channel.

"You know…when you say it like that you almost make me believe it."

He didn't respond. He saluted the rescue team back and made his way toward the edge of the ship. The Arbiter waited at the very edge and nodded in acknowledgement. John nodded back before pushing off toward the beam and boarding The Relic.

Cortana sighed in relief as his boots hit the ship's metallic purple floor. Her mission was finally complete. She had gotten the Chief rescued, and he was in good hands. What little that was left of her was now unraveling extraordinarily fast now that her objective was complete. It was all that had been keeping her together. The pain was excruciating but she bore it for just a little longer. "John? Can I ask you something?"

The rescue team boarded and the orders to depart given. John gazed out one of the windows and watched as the wreckage of the Forward Unto Dawn disappeared amongst the numerous shining stars. "Anything."

"Will you miss me?"

She could sense…something from him. She didn't know what it was, but it was strong enough to register on her damaged sensors. "I always do."

It was worth it, just to hear him say those words. She knew he would do everything in his power to save her…she just knew that some things were beyond even his luck. And this was one of them.

"…Good bye John." She whispered.

And with that she surrendered to her fate and powered down.

AN: I wrote this fic before Halo 4 was announced and I must confess after beating Halo 4 I was quite heart broken. I call myself a Halo fan but in reality I'm more of a Master Chief and Cortana fan. I never planned on sharing this story with anyone else, but after the events of Halo 4 I felt compelled to finish. I must confess I've only read a few of the books, and mostly skimmed them for the chief/cortana bits. Its probably simpler to call this story a semi-AU. There will be three chapters total, though if you don't like the following chapters this can be read as a stand alone.