The feeling of Casey's lips on her own was only a partial distraction to Zoe as the energy within her grew stronger, shifting down to her abdomen where it seemed to spread out. Zoe let out a sensuous cry as she felt her insides suddenly feel as though they were on fire, a pounding heat in particular building up around her groin. She broke off the kiss for a moment and pulled back, looking down through the gap between their bosoms and gasping in surprise as she realized what was going on: her clit had become engorged, puffied larger and erect, now out of proportion with the rest of her body. With each heartbeat coursing through her demonic body it grew little by little, longer and thicker and a bit more painful as more and more blood and whatever magic was behind this poured into it. Both Zoe and Casey let out a gasp as it slid up against Casey's skin, neither of them prepared for just how sensitive it would feel. But what would seal the deal is the realization that the tip of it began to mold itself into a mushroom shape, and Zoe could feel some kind of liquid start to secrete from it.
"Is that...what I think it is?" Casey asked, herself becoming a little unsteady as her own body seemed to jump and tremble with excitement of her own.
"I..." Zoe brought a hand down to confirm that she wasn't hallucinating, and a wave of pleasure sped through as soon as she got a hold of it. "I have a penis now." A part of her was still attempting to comprehend that statement, even as another part thought that of course this was a thing succubus magic could do. But most of her was operating on one base-level objective: finding satisfaction. Zoe was operating on auto-pilot as she closed back in on Casey, using both hands to grab hold of her and push her dick into Casey. By the time Casey's "Oh!" brought Zoe's mind back to the present, she realized she was already partway inside her friend. A bout of guilt passed over Zoe. "Casey! I-"
"More! Give me what I want, Zoe!" Casey had apparently become more assertive in her new demonic form, bringing herself closer to Zoe and wrapping her blue arms around the red succubus' neck. The sudden move ended up being enough momentum to send the two entwined lady devils tumbling to the floor, Zoe onto her back and Casey right on top of her. "Oof!"
The awkward landing didn't hurt for more than a moment, the rising heat and desire soon overwhelming that as their breathing and heartrate skyrocketed, both of them feeling Zoe's penis growing larger and longer within Casey, both of them feeling their own bodies' juices churning and moving within them. Casey adjusted her limbs to be able to get her weight off Zoe for the most part, though she remained on top of her as she began to caress Zoe's left breast with her hand. Zoe reciprocated on Casey's right, and it wasn't long before they went to teasing each other again, further driving Zoe's adjustment until something within her made her seize up. "Zoe?" Casey asked, stopping for a moment out of concern.
"It's coming, Casey!" Zoe felt a rush of energy flowing down to her groin as her hips began to thurst forwards towards Casey. Casey's body responded by bucking forward as well, sliding down Zoe's shaft just a bit more and the sides of her vagina clamping firm as Zoe felt the energy building up within her -- actually, in two places within her -- before a sudden burst rushed through her penis and into Casey. "Oh, yes!" Casey responded with a spurt from her own body, and then Zoe let loose another; this back-and-forth went for a few rounds before it began to die down, the two of them remaining where they were as Zoe's demonic penis began to retract from Casey, slowly losing its shape and size as it returned back to being a feminine clit.
Both Casey and Zoey were exhausted after another round, even with the inhuman stamina they had gotten. Casey slowly pulled herself off Zoe, lying on her back next to her demonic lover, friend,...and father? Mate? "Zoey?"
"Casey? How you holding up?" Zoey managed through heavy, exhausted breaths.
Casey managed to let out a tired laugh. "You don't sound like a woman who's just fucked someone with a dick for the first time," she quipped. "You sure you haven't done this before?"
"Heh. Maybe I'm just quick to adapt." Which, if Zoe admitted to herself, is probably the reason this whole thing was even possible -- quick thinking while keeping a clear(-ish) mind. She hadn't heard from the demon in a while, though -- whether it was now gone, off sulking in the metaphorical corner at being bested again, or biding its time, Zoe didn't know. That wouldn't come back to haunt her, hopefully...right?
Meanwhile, Casey brought a hand up to her stomach, feeling what the results of her impromptu wish had gotten.