Good grief, this story has been fighting me hard. It is shocking difficult to recharacterize someone you've been writing for over 3 years. But I'm giving it a shot. I'm not sure how quickly chapters will come out. Like I said, this story is fighting me some (it's aptly named), plus I'm teaching a class all by myself for the first time ever (simultaneous cheer and panicky flail) AND I'm trying to get my qualifying paper finished by the end of the summer. I'll do the best I can.

For those who haven't been introduced to Onslaught before, welcome! I hope this first chapter isn't too confusing. Let me know if it is. It will get better.

For those of you who have read my other Onslaught stories, hi! *waves* This Onslaught will probably end up being different than the one in my other stories. Not crazy different, but different all the same. Different events shaping him and all that.

Also, unlike my other Onslaught stories, this one has almost no basis in the comics. I tried, I really did, but I couldn't work it out with the other Onslaught story lines without making it a copy of at least one part of my other four stories. Which also makes this my first story with Onslaught where all of the plot not based in the movie is coming from my head. We'll see how it goes.

Special thanks go out to icanhearthedrums and aeskis for letting me bounce ideas off of them.

No copyright infringement intended. I don't own X-Men. Sadness.

Also, there will be spoilers for Days of Future Past. So many spoilers.

This picks up rather in the middle of things...as in smack in the middle of the movie. It should be fairly obvious what scene it is fairly early if I did things well.

Chapter 1: Behind the door, should I open it for you? (Metallica, "The Unforgiven II")

One moment, Charles was sitting in Cerebro. His head and heart throbbed in time with the failure of the ability he'd controlled since age 12 and his fingers rested on the temples of a man whose faith that Charles would become some kind of great leader of the mutant cause was as unshakable as it was inexplicable.

The next, he was opening his eyes laying on a stone slab. Stained glass windows cast a muzzy golden glow over the…was it a room? More of a temple really. He sat up. There were two older men in front of him, two younger mutants at his side. The young woman - it must have been her mutation that brought Logan's mind to the past - was injured. He couldn't tell how, but she was obviously in pain. The young man at her side was trying to help, casting worried glances at the shaking woman's face every now and again. Friends, then...possibly more. They weren't even alive yet in Charles' time.

The two older men, though, were familiar. The one standing at the back of the other was obviously…well, Erik was stubborn. Of course he would keep the same cape for decades, well into a dystopia in which a cape would be neither productive nor imposing. Even here, in his own future, he couldn't bear to look at the man who had lost him so much.

He stood from the table. The man he leaned in front of was safer ground. He was almost positive of who it was. A glimpse at his eyes would confirm it-

"Charles," the man said, meeting his gaze.

The long-abandoned scientist within him scurried forward with a startled laugh. Because it was indeed startling, meeting oneself.

"Charles," he replied. As quickly as it had come, the novelty of the situation trickled away. He glanced around the room again. "So this is what becomes of us. Erik was right. Humanity does this to us."

His older self bestowed a humoring smile on him, one he'd given students when they'd been brave enough to speak up in class, but didn't answer the question quite correctly. "Not if we show them a better path."

"You still believe?"

"Just because someone stumbles, loses their way, it doesn't mean they're lost forever." There was more to that mantra, he could tell, but he didn't know this face, his own mind, well enough to read into what it was. "Sometimes we all need a little help."

Help. He used to think nobody was beyond his help. Naivety at its best. "I'm not the man I was. I open my mind and it almost overwhelms me."

The smile turned sympathetic, understanding. It struck him that his older counterpart had been where he was. How had he escaped the void of hopelessness? What happened in this older man's past, Charles' future, that spurred him to recover, to live again, to work with-

"You're afraid and Cerebro knows it."

"All those voices. So much pain." Tears were rising. There was no point in tamping them down. As if he could hide anything from the man in front of him.

Older Charles hesitated, asked permission with a barely perceptible look. Charles met his penetrating gaze head on. Older Him wanted to see everything. How could Charles deny a man trying to save his future? Permission given, he could feel Older Charles peaking around his mind. He flipped through memories of the past few days. Logan finding them. Breaking Erik out of prison. The plane. The disaster in France.

Older Charles' emotions were concealed, but still Charles could sense them. A thrill that their plan to get Logan back had worked. Fondness for the boy Logan had introduced them to – Peter (how anyone could be fond of the kleptomaniac, Charles didn't know). Pain at the confrontation between Charles and Erik on the plane (they'd fought many times, Charles could tell, but seeing it from the outside brought new perspective). Resignation after Erik had attempted to kill Raven. Resignation? As if he'd been expecting to fail.

Then Older Charles was gone, and they were blinking at one another from the golden room again. The older man took a deep breath, let it out, cast a barely-there glance to the unresponsive man at his back, then came to some kind of decision.

"It's not their pain you're afraid of. It's yours. And as frightening as it may be, that pain will make you stronger. If you allow yourself to feel it embrace it, it will make you more powerful than you ever imagined."

Charles pulled back, revulsion spreading as the true meaning behind his older self's words sunk in. "You cannot mean-"

Older Charles continued to look at him serenely. "That is exactly what I mean. It's the greatest gift we have."

"Gift?" Charles sneered. "To call him a gift- what happened to us?"

This could not be him. He would never-

He was pacing now. What could have happened to him that his older self was so willing to speak of their…pain…as if it were a blessing?

"Look at me, Charles," the deeper voice said from beside him. He was too lost in his own thoughts to process it.

Something must be wrong. Erik…Erik must have corrupted him somehow. "No! He – our pain-" he spat, "is not worth this. Whatever future you have, He will only make it worse."

"You forget that I've lived with him far longer than you have."

That stopped him in his tracks. "Lived with Him? As in-"

"Cooperated. You have no idea the power you have within you. I didn't find it until years after where you are now and even then…there were extenuating circumstances. Keeping him locked away is only making him worse. If you accept him, you can be the end to the war we so desperately want to avoid."

Charles huffed a laugh. Older Him was a bit egotistical, wasn't he? Perhaps Erik had worn off on him more than he thought. "How do you know he won't go mad? Last time- Last time he tried to kill a man, maimed another-"

"Allow me to talk to him. We can come to an understanding."

Charles hovered a few feet away from himself. He'd never been good at covering his distress, knew he was given away by his hitched breathing and the look of terror-indecision-consideration etched over his brow. If he did this…if he let his older self talk to Him then that would be it. Because once that talk concluded, there was no way He would allow himself to be locked any longer, not after he'd been acknowledged after so many years of neglect. He was already angry at Charles for letting their telepathy go to waste.

His older self was trying to make it seem as if Charles would have the final say afterwards. As if he could talk with Him then come out and discuss it with Charles and have Charles decide what to do.

They both knew that wasn't the case. The decision was to be made right here, right now.

The prospect of unleashing Him on the world was not a good one. In fact, it was rather terrifying. But…he could feel the bare edges of what was happening in the future…what had happened to get them here. He could see all of Logan's memories of the Sentinals. Their friends would die. Most of the population would be wiped out. For the first time, he glanced at the figure he'd been so meticulously ignoring. He would've recognized the man even without the cape. Erik Lehnsherr had always carried himself with the grace and power a leader should. And here he was, standing at Charles' back, the pair of them working together to avoid the horrors of the future he himself could only catch glimpses of.

Not to mention how difficult it was living with Him in the background. It was always a struggle, a constant fight he knew he would never win until the day he died. It would be so much easier if he gave in. If his older counterpart was to be trusted, it wouldn't be the end of the world…

He was so tired of fighting.

Without a word, he moved toward his older self again in measured steps and resumed his previous position, meeting his own older eyes once more. Old Charles smiled and put his fingers to Charles' temples. No going back now.

He'd forgotten the bewildering combination of chaos and order that his younger mind had been in 1973. He ignored most of it. There too much pain, too much hopelessness, too much of himself concealed, and time was of the essence. Finding the cage he knew to be his goal was easy despite the fact that the cage hadn't existed in his own mind for decades. He stood before it in the blink of an eye. The cage's occupant shot to his feet. The figure was at the bars separating them between one blink and the next.

An almost perfect replication of his younger self gazed neutrally back at him. Not the tired, broken Charles who had spoken with him moments before. This was like looking into a mirror and finding 1962 staring back at him.

It made sense, he supposed. He'd started the serum not too many years after '62, long before he fully surrendered to the hopelessness pervading the other Charles. With his telepathy gone, the creature standing before him would've gone with it, frozen in time without the ability to evolve with Charles. His short hair was perfectly in place. The blue cardigan and perfectly ironed pants he wore betrayed nothing of the sinister features that made the entity so dangerous; the fact that those features could be so easily obscured made him even more so. The only thing betraying his true nature was the burning orange aura that surrounded his body and the eyes the glowed like coal in a fire.

After a preliminary once-over (squaring up his potential adversary…everyone the creature met was a potential adversary, after all), the entity settled himself, hands locked behind his back.

"And who do we have here? I haven't had a visitor in, well, ever," his younger doppelganger said. The voice was crisp, sharp in a way that had been missing in the Charles of 1973.

"Come and see," Charles said with a tap to his temple. "I have nothing to hide."

The man in the cage hesitated. Charles could read the internal battle (Is this a trap? If it is, should I spring it? If I do, can I still gain an advantage? If I don't, what do I lose?), before He, as Young Charles so humorously continued to call it, narrowed his eyes. Charles opened his mind and let him flick through.

It was almost comical to watch the entity's face. His gaze was distant, but his blinking and breathing became more rapid as he stretched, greedy to take in as much information as he could as fast as he was capable. When Charles felt He'd had enough, he nudged the entity from his mind. It stumbled back, gasping and staring at Charles with wide eyes before his mask slid back on with a minute shake of his head. Another blink and He was back at the cage bars again, hands behind his back same as before, this time with his head tilted in curiosity.

"And what is Charles doing with his mind in the future? Better yet, why are you visiting me? We both know that, of the three of us, he's the one who needs a guiding light."

"A guiding light is not what Charles needs. He needs confidence, faith that his ability can be his own again. Things I suspect you have in excess."

The entity quirked an eyebrow. "Do I?"

"I know you and Charles better than either of your know yourselves for the time being. The future needs our help. We, Erik and I, trusted our younger counterparts to perform the task, but the situation has become tenuous. I cannot lose the opportunity to ensure the safety of our future."

"And you believe I'm the way to do that?" the entity said, incredulity barely concealed.

This time it was Charles quirking an eyebrow. "As I said, I know you better than you know yourself at the moment."

The creature ran a hand through his hair, sparing a glance at the bald head before him. As soon as he noticed he was being observed, he stopped and resumed his previous position. "You say you and Magneto trusted your younger selves with the task, yet here you stand. I can't help but wonder if perhaps Erik had more faith than you for once. This was not a spur of the moment decision."

"It wasn't."

"You're not as optimistic as you let on."

"In ensuring that our future is saved? Optimism is best practiced when one uses all the resources at hand."

"I'm a resource to be used? You would let me out, give me a taste of the world, then what? You expect me to do your dirty work and go back into my cage with a pat on the head," he entity spat, turning a full spin with open arms, a mocking gesture at his quarters. "I'm not a pet." With that, He slammed back against the bars, grasp white-knuckled on either side of his head that would have shoved through the gap had it been wide enough. "If you let me out, I will not be imprisoned again. I will do what I must to ensure that."

Charles gave Him the same serene smile he'd bestowed on his younger counterpart. "We don't expect you to go back."

The entity pulled back with such force he stumbled a few steps away. "You would willingly free me knowing what you know of me?"

"You will not be allowed to do anything...rash."

"And who will stop me?"

"Charles will."

The creature scoffed. "His mind is already weak." He walked the length of the cage and back, running his hands over the bars. "The only reason I haven't escaped is because these defenses are the same ones he set in his prime. I'll lock him away as he did me. You'll never see the light of day again."

"Then Erik and Raven will stop you. You are not as omnipotent as you like to think yourself."

"You expect me to believe that our sister and a man who can move a bit of metal could kill me?"

"Kill you? Perhaps not. Defeat you, most certainly."

The entity narrowed his eyes again. "There is no difference. Defeat comes only in death." He ignored the knowing smile that crossed Charles' face. "Regardless, somehow I don't think you came back here to sacrifice your younger mind to me."

"Indeed I did not. I have a proposition. Work together with Charles. When your task is finished, he will allow you to remain uncaged. To share his mind. Neither of you would be trapped. You would both have free reign."

The entity was quiet for a moment, staring at the man before him. "You must be truly desperate if this is the plan you sacrificed your X-Men for."

"You've seen what the future holds. You know the situation is dire. I would not have wasted our chance at saving the future if I did not have absolute faith in this plan working."

"Your faith has always been the problem."

"Beneath all the desire for domination instilled in you, you have your own desires. Freedom. Acceptance. I'm offering you that. They will last far longer than even your most successful attempt at domination."

The entity was silent, contemplating, wary. "You can ensure that Charles won't imprison me again."

"As you said, his mind has been weakened over the years. He has lost his hope. Hope that I wager he's managed to pass onto you." The creature finally dropped his gaze, moving it to the wall and giving it a casual once-over, running his hand down a crack in the rock. Charles continued, "We need him to hope again. You are the answer. Do we have a deal, Onslaught?"

His younger visage stood back, keeping his eyes on the wall for another moment before returning them to Charles, narrowing once more. Charles stared back, open, allowing Onslaught to look through whatever he liked. A leer split the entity's face. "Onslaught. I like that." Onslaught's eyes focused on something behind Charles. "What do you think?"

Charles turned to find his younger self standing ten feet behind him. His expression was somewhere between fear and resignation as he stared at the entity in the cage.

Old Charles stood to the side to allow Young Charles to come forward, eyes never leaving his doppelganger. He didn't stop until he was inches from Onslaught's face. Emotion poured off of him. Old Charles could feel it, remembered how open he'd been despite his best efforts to forget it.. The early 1970s had been dark for him, perhaps darker than any other time of his life. Even when Erik had tried to use him to commit genocide against humanity and left him to die as Raven stood by and did nothing, he still had his school to pull him from the shadows of hopelessness.

Young Charles took the time to look Onslaught over head to toe, slowly, taking every detail in. "I spent so many years fighting you. You've caused me nothing but pain. Pain and suffering."

"Yet, without me, what kind of man would you be? Certainly not the upstanding citizen we used to be before you locked yourself away and destroyed your greatest gift."

"Ha," Young Charles laughed humorlessly. "You sound like Erik."

The orange aura flared, then settled. "He is misguided, but he is not wrong about everything." Onslaught's demeanor shifted from uncompromising to imploring. "I can help you, Charles. I can make the pain bearable. Let me. Let me help us."

Charles recognized the tone immediately. Onslaught was a complicated creature, a devastating concoction of manipulation and genuineness. One could never tell how much of either one was receiving. It was a code even he hadn't cracked, and so he had no way of telling whether the Onslaught now genuinely wished to help his other half or if he was taking advantage of a situation already tipping in his favor.

Young Charles was silent again, probably trying to puzzle out exactly what Charles had been working on himself. He closed his eyes, sighed, reopened them with resigned determination. "I will free you because I cannot fight you anymore. As soon as the serum wore off, it was as if you'd never left. I can't- I can't anymore. He," Young Charles gestured at his older counterpart, "says we can work together. If it will save us from this future, then I will allow it."

Onslaught's face split into a grin. Young Charles turned to Charles. "I certainly hope you know what you're talking about."

Charles gave a nod. It was done now. Erik would perhaps be less than pleased, but he'd made plenty of decisions without Charles' input. This was for the best. Yes, the probability of Onslaught rebelling were high. Very high. But the entity would do what he had to to save the future before he did so. That much Charles knew. Onslaught had gotten them far in the war. If Charles accepted him earlier who knows where they would've been.

Yet he also knew how his younger self would see the situation. The future now rode on the shoulders of a being who, before Young Charles started losing his hope, was the equivalent of a psychopath that quite literally had the ability to control the world. He had faith it would work. Absolute faith, as he said. But faith, by definition, meant taking a leap into the unknown.

Young Charles pulled a key from his pocket and fit it in the lock. With Onslaught practically vibrating on the other side, the door swung open.

Logan felt when Charles pulled away.

"Find what you were looking for?"

Chuck was staring at him, not saying anything. Shit, had he messed up again? Really, any other mutant would be better suited for this. He'd told them patience wasn't his strong suit. Neither was helping those who were lost. What had he been thinking? Was he even helping or was his future even worse than it had been?

And what the hell was that?!

He could've sworn an orange flame had flared behind the telepath's eyes. Leaning over, he tried to look again, but the man had shut his eyes and had a hand to his head like the few times he'd overused Cerebro early in the war, back when they had a chance of saving people. Logan shook away the memory.

"Professor, you okay?"

The Professor's eyes fluttered open again. It almost seemed like he was watching for a reaction. There was none to be had. The eyes were the same blue as they had been before. Must have just been a trick of the light. But then why was he watching for a reaction? Had he been freaked out by what he saw in the future? That had to be it. Nothing more. Right?

Hank must have figured out the lights because they flickered back on. Sure enough, the kid strode back into the room not two seconds later.

"Power's back on."

Thank you, Captain Obvious.

Charles smirked. Odd. He looked almost smug. Then again, Logan had never been the best a reading people. That was the Professor's job.

"Yes," Charles said.

As the telepath turned to head back to Cerebro, his two companions were deprived of the chance to see his eyes flare brilliant orange again.

"Yes it is."

All the dialogue in Young Charles' first interaction with Old Charles ("Charles" to "...it will make you more powerful than you ever imagined.") is directly quoted from the movie.

I feel like Inception just happened. Old Charles is in Young Charles' mind while Young Charles is in Logan's mind. And hopefully having 3 versions of Charles didn't make this incomprehensible. So many pronouns and referents...

Reviews generally help me write faster. Let me know what you think!

Also, forgive any errors or repetition. This is unbetaed.