Erik had been through a lot of trials in his life. None of them had been like Charles Xavier.

Perhaps it was unfair to compare someone as genuine and sweet as Charles to the other things he had been through—to Shaw and his tables with straps and his implements—but at times like these, when faced with the full force of that sincerity, he found that he had even less defenses against it than he had against Shaw. With Shaw, he knew what to expect. With Charles, he always felt lost. Off kilter.

Charles was all warm hands and gentle words, then at once a fierce insistence that Erik was worth it, that he belonged there with them. It was enough to give one whiplash, were it not for the fact that it was all so irrevocably insistent of his own goodness and worth as a person. If he could expect nothing else, he could expect whatever Charles would do to go in that direction.

That did nothing to help him right now. Days ago, Charles had asked him, so calmly, so sincerely, if he was allowed back into Erik’s head. To help him train, ostensibly, but that was only part of what had happened. He had reached into Erik’s memories like reaching into the reeds of a pond and pulled out something so precious to him that it might have been made of gold and physical between them. A memory of his mother, of celebrating with her. Being safe with her.

It rattled Erik at first. Knocked him off his pedestal of anger and hate and had him face-plant right into the soft grass of whatever this was that he had with Charles. But then he had began to realise the similarities of it to what was happening here. With Charles, he was not afraid of being betrayed. In Charles’s house, he did not fear waking up with knives in his flesh and Shaw towering over him again.

Was this safety? It was not exactly the same as that memory, but it certainly felt close to it. With Charles, he found himself able to smile. To relax. He should really known better than to do that.

Not because he was betrayed, but because Charles could be playful when he least expected it. Erik had no idea how to deal with that, no practiced defenses against it.

They were out on the grounds that day, hidden amongst the trees around the lake. Charles was watching him as he trained, levitating various bits of metal they had found around the house, forming complex shapes around himself and the rustling trees. Charles had informed him that one of those trees was his favorite, from his childhood. What a ridiculous concept. He still took a little extra care not to graze it with the odd pair of scissors flying about.

They were alone out there, in part thanks to the ridiculous comments Raven and Alex had offered the one time they were allowed in on Erik’s training (it was not juggling, damn it). Mostly, though, it was just nicer to be out in the quiet, and Charles only offered his opinions if he thought it might help. This, Erik was quite proficient at, and so the professor remained still, sitting in the grass behind him. At least until he got an idea, as Erik would soon come to learn.

The metal was forming a snake that slithered around him in the air, curled over the canopy of the nearest tree, and twitched to a stop in the air as Charles’ voice sounded behind him. Erik turned to look at him, arms still outstretched in the other direction.

“I was wondering,” Charles said, “if you wanted some help with your practice.”

Erik raised an eyebrow. “Oh?”

In response, Charles raised his hand to his head, wiggling his fingers next to his temple in a familiar way.

“Test your concentration, perhaps?”

They both knew very well what kind of focus it took to use their respective powers. It was a correct angle from which to approach helping, but what exactly was he suggesting? Erik frowned as he watched Charles rise to his feet.

“Keep going,” he said, nodding his encouragement. “It’ll become clear.”

There was something in his expression that put Erik on edge. He knew that playfulness by now, but it came in so many different forms. Still, he turned back and guided the metal snake to curl around the trunk of the tree and slide back down. At the roots, he began to split it into tendrils that curled in different directions.

Then something brushed up his side, light as a feather.

He startled, convinced that something that lived in the trees or bushes had found its way into his shirt. The metal stalled, but did not fall as he reached down to smooth his sweater over the area. When he felt nothing more, he turned his attention back to the metal.

It happened again, almost immediately. This time, it was two quick swipes, up and down his ribs. He brushed at it once again, and found that this time, it didn’t help. The feeling didn’t dissipate.

Confused, he turned around, immediately spotting Charles, fingers at his temple and a smile on his face.

“What’s wrong?” he asked, impossibly innocent. “I thought you were focusing?”

Stilling the metal in the air, Erik raised an unimpressed eyebrow.

“Really, Charles?”

Charles gave a shrug, and his fingers stayed in place.

“All’s fair in love and practice.”

Erik raised the other eyebrow then, and his sudden burst of amusement was clearly felt by Charles, whose smile widened the slightest bit.

“I’ll make sure to remember that the next time you’re training,” he said.

He turned back to the metal, but not before he could see Charles open his mouth and find no retort. The sound of him trying was almost imperceptible, just an aborted breath or two, but Erik noticed. His smirk, however, did not last for long after that.

Charles was evidently done being subtle, but Erik was stubborn if he was anything. The next touch moved up both sides, and it felt more like fluttering fingers than feathers. Erik’s arms clamped immediately down to his sides, the metal made a jagged motion sideways, and he clamped his mouth shut. At his armpits, the feeling dodged up to his shoulders instead and cascaded like skittering nails down his back. It made him shiver more than anything, and he was going to have to ask Charles to do that the next time he needed help sleeping, but it did not break his concentration.

If Charles was noticing the way the metal shivered in the air, he said nothing about it.

Slowly regaining his confidence, Erik selected a smaller section of the metal—a haphazard mix of scrap parts and loose staples that wouldn’t be missed. Everything else lowered to the ground, and he brought it closer to himself, letting its parts curl around each other and melt into one uniform piece. Curling his hands in the air around it, he began to form it into a cube.

Something curled teasingly over his lower ribs and down his sides, heading with singular purpose towards his hips. He would never admit to the sound that escaped him as he realised that.

It didn’t stop, and Erik fought for his life. The feeling curled like gentle nails over his hips, and he suddenly felt less like training and more like curling up into a ball and disappearing. The compromise between that and his pride was his knees bending halfway to a crouch and his hands shaking as he struggled to hold on to the metal. He clenched his teeth, refusing to let out another sound.

Then that something--that nefarious, nebulous feeling—turned without warning to a pinching squeeze around the base of his hips.

The metal cube followed him down to the grass like an obedient dog as Erik came to the conclusion that the best solution here would be to hunker down like a crumpled hedgehog and suffer through the feeling. There was another sound, not a laugh, but some sort of whine, then a strangled “Charles”.

There was a chuckle from behind him, warm like honey and sweeter, still. The feeling didn’t let up, even as he let go of the metal to cover himself uselessly with his hands. At his first breathless laugh, as though it was the trigger of a gun, Charles let loose with it.

Hands or feathers or something else entirely—Erik was too far gone to tell—skittered and danced up his sides to his armpits, down over his thighs, rolling over his belly. Erik made a sound like a wounded animal and descended into giggles that no one but Charles would ever find out he was capable of. It felt like torture. It felt light and warm. He was unable to make any sense of the feeling.

“Chaharles,” he pleaded, his voice higher than he had ever heard it before. There was another laugh from behind him, this one louder and delighted, and Erik was not so far gone that he couldn’t appreciate being the reason for Charles to laugh like that. For a moment, the sounds mingled, like harmonizing notes. Though the result was nice, Erik felt a little bit like he was actively dying at this point.

He had never laughed at length, had never had reason to, and while Charles had tried tickling him before (likely the reason he dared to do it now), it had never been this intense. Erik found himself lying sideways in the grass, an imperfect metal cube forgotten in front of him. It watched him impartially as Charles methodically took him apart. He could do it from a distance. He could do it without lifting a finger.

He was terrifying, and Erik would be turned on about that if he wasn’t so busy giggling like a child.

“What?” Charles asked, and the laugh was clear in his voice. “I thought you wanted to practice!”

His tone lowered a bit, but he was no less amused when he added, “You look lovely like that, by the way.”

Erik realized with some difficulty that Charles was teasing him, and was that not just the cherry on top of all this? He had run from a lot of things and fought through a lot of things, but few of them were as paradoxical as this. This should be humiliating, and he should be lashing out. Instead he felt completely safe, a feat only ever possible because it was Charles doing this. Charles who had proven as much as one could that Erik could trust him. That he wanted him to feel safe and comfortable. And apparently to be tickled beyond coherency.

He knew that Charles was at least shallowly in his head now, keeping what boundaries he could while making sure that Erik wouldn’t be overwhelmed. But to hell with that, he thought. Clearly, training was over, and this was nothing if not a provocation.

His laughter had gone from a loud, boisterous thing to a breathless sort of wheezing at this point, and it was a struggle to move at all with the feeling creeping all over him like vigorous ants. Still, Erik was a stubborn man, and Charles had not been careful that day. He was still wearing metal. A watch on his left wrist. Cufflinks. A pair of slacks with a metal zipper. All enough for Erik to reach out with one swift, uncoordinated hand and yank him gracelessly through the air as Charles yelped like a startled child. The tickling feeling disappeared in an instant, and Erik had time to take one breath before Charles landed on him with all the grace of a man tumbling off a cliff. It was all Erik could do to raise one arm and try to catch him, but they still ended up in an uncoordinated roll across the grass.

“Erik!” Charles was yelling, but they had slowed to a stop and Erik was already ensuring that he ended up on top. Surely, Charles was going to say something about this being childish or their clothes getting dirty, but Erik was faster. The next sound Charles let out was a loud, startled laugh around his next words.

“This—ah—thihis is nohot part of ihihit!” He was flailing, reaching for Erik’s hands, but vengeance gives one reflexes like no other. Erik dodged him at every turn and dove inside that neat jacket with no preamble to find the soft skin of his belly. The laughter raised an octave as Charles tried to curl up like a shrimp, and Erik grinned triumphantly down at him. In the next instant, Charles’ hands had been yanked above his head and pinned to the ground by watch and cufflinks both.

“All’s fair in love and practice,” Erik parroted, smug beyond belief. He could feel the whispers of tickles over his thighs and hips, but Charles was too distracted now to make it all that effective. Erik huffed.

“Come on. You can do better than that. Show me your legendary focus, Charles.”

Charles did no such thing. Instead he curled sideways as much as he could and laughed his head off, eyes shut and cheeks red. The sight of him so loose and carefree was almost enough to distract Erik from the task at hand. Almost.

“We’ll keep at this until you can get out, you know.” He did not imagine the way Charles’ breath hitched between laughs. “Show me your escape strategy.”