It is better to view this particular story on AO3 as there are certain formatting issues that, unfortunately, can't be displayed on FFN and thus rather mess up the story itself. On AO3 I am TwinKats and this story is titled Aftermath. I would link, but FFN has disabled that option.
Aftermath
Chess
He sits alone, chess pieces set out in a game that has been in play for years. Fingers clasp a rook, crisp blue eyes (OCA2 gene, groovy mutation) distant in thought. The gloves on his hands are rough (winter in Russia, '62, Charles) a grey cotton-wool fabric but suiting for an old man his age in the not-quite-winter but no-longer-fall weather that has taken New York. He's waiting for White to move (no, God, Charles you fool!) but White never will, he knows. White is dead (like mama, only worse, infinitely worse) and he's left with an unfinished game and his brooding thoughts (memories), powerless.
(no, not quite powerless, not really, because he knows so much, too much, Nazi hunter, killer, Frankenstein's monster, where is his creator?)
He finds it funny how without the helmet, the pink and red and grey (gaudy, he admits, only to himself) costume he paraded around in, virtually no one recognizes him. It's comforting and unsettling all at once, and he can't help the (not-quite shark-like) grin at those thoughts. Isn't that the story of his life? His fingers toy with the rook a second longer (he wishes for a hand to twine them in instead) and he lets go with a sigh. It's late, time to pack up—
(next time, Charles?)
—to head back to the—the—well wherever it is because it's not home, not really.
(home was with him, his equal, his opposite and perfect and not alone, god you're not alone)
He'll be back tomorrow, waiting for the other, his White King that will never come, to finish a game that will never be done.
(for how can it really be over when they were playing as well as acting and the Red Queen killed her White King before turning Black? That wasn't how the game worked after all, the pieces can't do that, she can't do that!)
Tomorrow he'll come back, set the board up, wait, reminisce, remember, and then go back to his not-home to repeat. Maybe White will show (White has to, has to, because he can still move Black without touching, despite all odds he pushed that Bishop, he did) and they'll laugh about everything and play and then go home, together, like they should have that day in Cuba.
(all he wants is to go home, to curl up and wrap his arms around his not alone and ignore the world because the world can rot, he is done with it, with everything, after all the world stole Charles from him, ripped away just like mama but oh so worse and oh so painful and Gott un himmel he just wanted Charles back. He'd taken being powerless and with Charlesthan powerful and without)
His name is Erik Lehnsherr (Magneto, the mind traitorously whispers) but he is nothing (just Black and lonely and old, god when did he get so old?) and has been nothing (he refuses to be mutant without Charles) and will remain nothing.
(because kliene Erik Lehnsherr, because Magneto, because the mutant who could bend metal and manipulate magnetic fields, is dead and has been dead ever since he lost Charles Xavier. His body just didn't know it. Neither did his mind, really, but his heart knew and it bled and fluttered but did not beat)
Summary: He can't fathom how their game got so twisted, and turned out so wrong. Chess wasn't supposed to be like this.