A/N: An really brilliant Anonymous person asked for this prompt:

"AU, x-men first class. Same plot as the movie, only in this universe Shaw is Charles' father. Charles is rebelling against his dad to stop WW3. He meets Erik the same way as he did in the movie, though he is shocked when he finds out about what his father did to Erik. Charles doesn't tell Erik that he is Shaw's son. Erik eventually finds out. (How he finds out is up to you. This can be Cherik or just Erik/Charles friendship. Bonus points for making Shaw a good father while still being a Nazis, human killing bastard.)"

And I don't know if I did this idea justice, but I sure as hell tried. ;D

Erik storms into Charles' room, not caring that Charles is half asleep.

"You deceitful bastard!" the metalbender roars, storming into the room with something in his hands.

Charles shoots upright in bed, flailing to get the covers off of him as he scrambles to his feet, his head fuzzy with lingering traces of sleep. "Erik? What is it? What's wrong? Did I do something to —"

"You're his son," Erik growls, the accusation like a knife in Charles' throat.

Charles tries to swallow around the dagger-like pain, and he feels his heart jump-start with adrenaline-fueled dread. He doesn't need to ask what Erik means. "…How… How did you find out?"

Erik throws down the object in his hand. It makes a loud echoing sound, the sort when a soft-cover book is flopped down onto the ground carelessly.

He snaps his fingers and the lightswitch is thrown on, and he kicks a foot backward to slam the door at a distance. "This," he hisses, pointing a finger down at the item, then snapping his head upward to look Charles dead in the eye, his finger now pointing into the air in front of Charles, an angry jerk at every other word. "It was in. The. File. Shaw's file. 'Only known relatives: son, Charles Francis Xavier, child from an out-of-wedlock encounter in England.' Your mother, carrying a bastard-child of a murderous bastard, just had to flee to the States, didn't she? And you grew up thinking, what, that you could right your father's wrongs, using me to get back at him?"

Charles recoils as if physically struck, and stares wide-eyed at his ally. "No, no," he says softly, pleadingly. "Erik, please… You know me better than that. I would never use you, I —" He chokes on his own words, unsure how to phrase them. So, instead, he opts to slip into Erik's mind to explain.

My father would visit my mother and I at times. He was always cordial to me. He treated me sweetly and was always proud of me and my mutant abilities, and he taught me how to expand my powers to the level they are today.

"Get out of my fucking head!" Erik howls, clamping his hands over his ears as if that would cease the sound of Charles' voice. "You don't deserve to talk to me. I don't care what you have to say!"

But the telepath gently presses onward, stepping over the thick manila folder to stand before Erik, whom flinches away.

I didn't know what he did to you until I saw it that night when I saved you. I'm sorry, Erik; I should have told you the truth, but I feared a reaction like this, and I didn't want to lose you. Not because you're some asset to me, but because I value our friendship. I care about you, and I want to help you rebel against my father and have him face the consequences for his actions.

Erik scowls and drops his hands from his ears. "No, Charles. That's not how it works and you know it. I plan on killing him. I plan on ending your dear father's life." He stresses the word 'ending' and adds a sarcastic snarl to the words 'dear father.' "Do you have it in you to allow that?" he snaps at the end.

Charles whispers, "No, I honestly don't. Killing my father will not bring you peace, Erik. And what's more, I don't want to see the man who stopped by now and then to help raise me die. I would rather he lived, locked away in some confined place where he can't use his energy-snatching mutation, rotting in prison, than be a cold corpse in front of me."

Erik takes a sharp step forward, his hand going to Charles' neck. He grips it and falls on top of the shorter man, pinning him to the floor. Charles doesn't struggle. He could easily reach into Erik's mind and make him stop if Erik tries to truly kill him. But as it stands, he is only using one hand, and he's breathing heavily, but he isn't increasing the pressure on Charles' throat.

"I never meant to deceive you, Erik. Please, understand that my sentiments are genuine. I want you as my friend, my ally. I want my father's plans to be stopped. And this… this isn't much, because I not like him. I —"

"Shut up," Erik says curtly, his words coming out from behind his clenched, grinding teeth. He leans in deadly close, their noses almost touching, and glares directly into Charles' eyes. "I don't listen to begging liars. You met me under false pretenses, Charles, and for that, I can never forgive you." He stands and releases Charles, starting to turn his back and walk away. "You're the son of my hated enemy, the man who made my life Hell. We can never be allies, never be friends; never again."

"No! Erik, don't think like that, I— I'm not my father! I'm nothing like him! Erik, listen to reason —" Charles hurls at Erik's retreating back, chasing after him to grab his shirt before he touches the doorknob and leaves. "You don't understand. Shaw is my enemy, too. My father, yes, but also my enemy. I'm on your side, can't you see?" he tries, desperately trying to begin or end something, whatever this is between them.

Erik whirls around, eyes cold, the usual glasz color a dangerous, steely green-grey. "On my side? If you want to be on my side, Charles, you have to know that your father is going to die, and that you will have to be willing to help me do it, because that is the only way to end him. He would break out of prison, no matter the confines. The man needs to die for all he's done and will do."

Charles swallows. This is too much to take, too great a burden to bear. In a small, wavering voice, eyes brimming with tears of tension, he says, "You know I can't do that, even if I know it's true."

"Then let go of me, Charles. I'm walking out of here right now, and I'm not coming back." And he's trying to pry Charles' fingers from the backside of his sweater, but Charles is gripping tighter and standing his ground.

"Erik, Erik, please —"

"Dammit, Charles, let go!"

"Erik, you need to know —"

"Shut up, just shut up! You are his son, and no matter how you try to hide it, part of you will always be like him!"

"No, Erik! I'm not, I —"

"Don't make me hurt you, Charles! There is pelnty of metal in the room to use —"

"Erik —"

And just before a letter opener from Charles' bedside table rattles out of its drawer and nearly flies into Erik's hand, Charles launches himself forward and wraps both arms around Erik, cutting off the man's actions with a grunt erupting from both their lips.

Braced against the door, Charles' face hidden from view, Erik hears, "I love you," falling from the telepath's lips.

Erik goes rigid, numb. "…What did you just say?"

"I love you, Erik," Charles restates firmly, his tone even and sure of himself, as steady as it would be were he to read his thesis or retell a scientifically proven fact. "I love you, and that wins out over the conflict I have of love/hate feelings for my father, and the responsibilities I have as a person caught in a position of blood bond versus my duty to the world to save it from men like the one I'm related to. So please, Erik, don't leave. And know that, no matter what happens tomorrow, I am with you and not him."

Erik's eyes scan Charles' face, the openness and pain reflected in those too-blue eyes, and he can see that Charles isn't lying. He isn't even acting, like Shaw always did, with false sweetness and mocked honesty to cover a lie. This is real. He can even feel it on the edges of his mind, Charles lingering there like a ghost.

"…You're abhorrently acting like a woman at the moment, Charles," Erik says, shrugging out of the telepath's grip and moving aside to run his hands through his hair. He's shaking, and he doesn't want to think about why. Leftover anger and adrenaline? Shock? Or the feeling that he isn't as repulsed by this new piece of information as he should be and wants to be? —But it doesn't matter, because he refuses to dwell on it.

"What are you thinking now?" Charles whispers. He doesn't want to upset or push Erik away by violating his privacy at a time like this. So he asks instead, hoping for a willing response.

Erik snorts. "I'm thinking that you're bit fucked up, Charles. You're in love with a man who has killed, who intends to slay your father, and partially hates your guts at the moment. That's quite backwards."

"Perhaps not," Charles tries as he runs his own hand through his hair and walks in his clammy pajamas over to the file folder on the floor to pick it up and set it down on his bedside table, the drawer ajar. He shuts it, a shiver run through him when he briefly sees the glint of the letter opener inside. He licks his lips and continues, "After all, the circumstances are unique. You've killed men who have done wrong, who have tortured or killed others, and maybe one or two were mostly innocent, but they were trying to kill you, so you did it out of defense. And as for my father… I hardly see him that way. Not anymore."

"…This is an argument that is going to go 'round and 'round in circles, isn't it?" Erik retorts. He peers over his shoulder at Charles, and the telepath nods his head. Erik huffs a bitter laugh. "So what now, then, Charles? Do I go to bed and pretend tomorrow that this never happened, act like I don't know? Or will you make it easy on me and make me forget?"

"…I would never do that!" Charles gasps. He shakes his head. "And I can't ask that other thing of you. Instead, I ask you not to tell anyone of this — Moira knows, however, since she read the file, being on the case and on the need-to-know list — but other than that, not even Raven knows, so I ask you not to bring it up in front of others. We will behave accordingly, and you are free to act however you wish. I won't hold back; I'll fight like all the rest of you. This is personal for both of us, but I don't plan on running to Shaw's side once we see him."

Erik nods, accepting this reluctantly, and isn't quite looking at the other mutant. "And what of your feelings for me? Am I expected to —"

"I expect nothing from you, Erik," Charles replies swiftly, clearly uncomfortable. "I only wanted you to be aware of my reasoning. And I can fully understand that you don't feel the same, for multiple reasons, sexuality being the least of them. So please, don't…" He sighs. "Just don't."

"Sexuality is the least of it, Charles, because I don't think I ever had one. No time," Erik remarks as he moves to pick up the file on Shaw, his forearm brushing Charles' side, making the telepath's breath hitch. "But before tonight, I did have feelings for you, ones that went beyond platonic companionship."

And with that, Erik marches out of the Charles' room, folder tucked under his arm, and the door shutting loudly behind him with a flick of the hinges.

Charles exhales slowly. He feels like shit.

.:.

"Don't do this, Erik!" Charles begs.

But it's too late. He feels the roaring sensation like having one's head shoved into a churning rudder of a ship or the propellers of a helicopter, and just like that, his mind washes cold and he knows. He knows.

His father — Sebastian Shaw, Klaus Schmidt, a dozen other names — is dead.

And the man he loves killed him, even despite Charles' remaining hope that his father's life would be spared.

It only hurts more when Charles thinks over and over again how he could have released his grip on his father's mind and possibly saved his life, but a sick, deep-rooted, dark part of him had held on because he didn't want Erik to die, and he wanted to watch his father be killed.