Erik can't get enough of Charles' ears and tail. They're new, and striped; he can't stop touching them, stroking them. Charles doesn't much care to have his tail petted - he keeps lashing it out of Erik's reach after a few seconds - but he purrs when Erik scratches him behind the ears.
"You look like a tiger," Erik says.
"More like a tabby cat, really," Charles says, with a dismissive wave of his hand as if he doesn't care; but the purring goes up a notch, giving him away.
*
"Much as I appreciate your renewed interest - and that I don't appear to be competing with Raven for your attention anymore, which is very nice - I'm really not sure this is the best idea," Charles says a little later, when they're both naked, Erik crowded onto his lap and trying to work out a position.
"It's a wonderful idea," Erik says decidedly. Part of him would actually like to get a better look at Charles' cock - he can't put his finger on it, but something seems different - but at the moment he just wants to ride it, while looking deep into Charles' eyes (it's not that he's romantic, but more that Charles' pupils are pinning, dilating out until they've blotted out his irises, then constricting again - it's the sexiest thing Erik's ever seen in his life).
"But -"
Erik isn't a patient man, and he's never wanted Charles as much as he does right now, but he does understand that sometimes people are insecure about their appearance, and may need reassurance. "You're perfect," he informs Charles; and then, that taken care of, he sinks down onto him.
Everything goes just as it should, until Erik begins to move, at which point: pain. There's not supposed to be pain - at least not that much.
Alarmed, Erik tries to pull off completely, but: more pain, and he's stuck, and he stops, holding himself as still as he can.
"What the fuck," he hisses.
"I tried to warn you, I really did. Along with the ears and tail, seems I've developed more of an, erm, cat-like penis. With, ah, barbs. Which you would have known if you'd bothered listening to me."
He doesn't sound nearly as sorry about it as he should. His eyes are still pinning, and his purring has become more of a rumble. How dare he.
Erik stays like that for a long moment, working up the nerve to try to sever from Charles again. When he does, it's in one swift jerk of his hips; he screams once (in pain), then keeps right on screaming (in rage) for half an hour afterward (there is no serenity in evidence). Charles tries interrupting a few times with statements along the lines of "well, they serve a purpose, you know. They induce ovulation in female cats," but stops after Erik's third or fourth, "I don't give a FUCK."
When Erik runs out of things to scream and languages to scream them in, he whirls around and stalks out of the room, swiping viciously at damp eyes as he goes.
He limps for the next week.
*
Three weeks later, Charles loses the ears and tail: they disappear just as mysteriously as they first appeared. Erik misses them, but the tradeoff is worth it, since life without bottoming is a tragedy, where life with Charles looking normal is merely sad.
"Are you really going to inspect my penis every single time we have sex from now on?" Charles asks.
Erik gives him a flat look, then bends back down to peer at it some more. It looks normal, but it could still be a trap.
*
Five weeks after that, Erik storms into Charles' study one afternoon, with the blood test results (courtesy of Hank) crumpled in his hand. He's still feeling a little green from spending half an hour on his knees in the bathroom for the fifth morning running, but the shakiness is from something else entirely.
"They induce WHAT," he says.