You dragged a finger down Sophia's spine, all the way down to where it merged with your own skin. You noticed goosebumps forming on your girlfriend's arms and, consequently, on the skin of your shared pair of legs as well.
Her back merged exactly where her spine was originally was supposed to end, at her tailbone. Her ass basically disappeared into your body, and further down was where the two of you shared sensations, feelings, touch, and movements. At times, you felt Sophia's conscious effort to stop fidgeting, and only then were you aware of it in response. Sophia had a tendency to cross her legs, where you felt awkward on how that seemed to make your genitalia, your new ones at that, fold in on themselves. It wasn't exactly flat down there.
Sophia's spine seemed to merge at the base of what was formerly your cock. Asking her to move around to test if she noticed anything, proved to do nothing more than having her shake your hips involuntarily. Thrusting your hips forward had the same lack of effect. You received no pleasure from it, so your cock must have disappeared, dissolved in her merged body, altogether, after the Fusion Wave washed over the two of you.
Now you were stuck. And even though the initial thought wasn't one that sparked a sense of doom, you and Sophia quickly began to realize the implications of basically being each other's conjoined twins. It wasn't the strangest of transformations you had heard of, but you'd have to take a lot of time learning and adapting to each other's habits and mannerisms, as you were stuck together, possibly forever. After all, you doubted that the Fusion Wave had anymore plans with you.
Walking went easier than you expected. It was as easy as having one person completely lose motor control over their legs, and let the other person do the walking. You understood why Sophia preferred to walk the stairs by herself though. Your shared sense of balance was still a little screwed up, and she was the front passenger of your conjoined body. Having such a large drop in front of her with 'dead' weight behind her, must have felt like she was putting her life in your hands, and she didn't see you as the most careful person between you and her. So, step by step, you learned to walk again.
Then came work. With the Fusion Wave, the economy, at least in the city, had gotten to a stand-still, until everybody was accounted for. Whatever chores you and Sophia had, you could work on some of them at home, but you no longer had much free space to work with anymore. Although Sophia could still sit behind her desk like usual, even if you were breathing right behind her neck, it still meant that, whatever papers you had to write, would require a little more effort.
Sophia proposed that you could lean to the right a bit when doing your job, while she could lean to the left, but even then, the bureau was simply out of reach at times. Reading seemed to be less of a problem, at the least.
For food and drinks, and getting rid of it, posed another problem. You and Sophia didn't share the same stomach or bladder, but you could only get rid of the stool in one way. Its implications were reasonably unpleasant to think about. You first realized this when you had to go to the toilet to pee, but Sophia did not. She was truly surprised when your shared muscles in your lower abdomen relaxed, and a steady stream of piss came out to greet her. You wanted to stand up quickly to get the toilet break done with, but Sophia was quicker to protest, and then proceeded to dab your vagina dry with some toilet paper. It was a habit you'd never taken up yourself, since you'd only have to stand in front of a urinal and squeeze anything remaining out once you were done.
Lastly, there was pleasure. It felt more like sex than just masturbation, when Sophia proceeded to touch your snatch down below. To her, it felt exactly the opposite. Sophia's hands were alien to you when she touched you down there, and to her it felt the same, when you rubbed your hands over your thighs, and felt up between your legs. It somehow had Sophia shaking, and in response, your pussy started becoming wetter and wetter than you'd expected it to in such a short time.
You relaxed your muscles, bathing in the pleasure, and enjoying watching, and feeling, Sophia squirm in your grasp. The building orgasm was a mutual experience, and you weren't even sure if it was fueled by your own pleasure anymore. It kept growing and growing, and even when you thought you were at that point, the pleasure didn't stop rising. Eventually, you felt wrinkles on your fingers, as they were constantly feeling around your wetter growing snatch.
Eventually, Sophia used her back to thrust your hips forward, pulling all the strength in her spine to pull your ass upward as well.
Finally, you reached peak orgasm, and you moaned in sync with Sophia's melodic voice, as your girlfriend drove her own hands into your pussy, and juices sprayed out of your crotch with each spasm she managed to inflict on your shared lower body.
Of course, Sophia ended up in your arms again, as you held her close in a tight hug, lying sideways on top of your bed. You couldn't call it spooning in its entirety, but you held her close anyway. To have to share a body with your lover like this, it felt like a blessing, rather than a curse.