I stepped away from the bed to fetch a mirror and noticed that the glow from my cock ring diminished slightly. Glancing over at Katherine's collar, the glow from that had lessened as well. It made sense that the closer they were together, the stronger the bonding effect.
Retrieving a mirror, I held it up in front of Katherine's face and angled it downwards slightly so that she would be able to see the change in her body. After lingering there for a second so that she had time to appreciate it, I put the mirror aside. I wanted to get a better look at her new breasts, and was about to sit her up to start the laborious process of clumsily taking her top off when I had a better idea. Grabbing a convenient pair of bondage safety scissors, I took a fistful of the fabric of her top in my hand, and cut a huge gash through the cheap fabric. With a few more snips it fell open, and her breasts spilled out. They were soft and pillowy and looked very inviting indeed. Placing my hands either side of them, I squeezed them together to form a deep cleavage, and pressed my erect cock, already quite a bit larger than its usual size, into the gap between the warm mounds until it disappeared.
"That's another thing to add to my mental list of things that I want to do to you. But first, I've been thinking about that mouth for a while."
I grabbed the plug by the base and slipped it out of her mouth, leaving it gaping open in an 'o' shape. I had wondered if touching the butt plug would cause my cock to take on its shape, but it did not. I guess that an object needs to be sufficiently phallic to trigger the transformation - I'd need to do some experimentation with that in the future. I lay Katherine back down on her back, and then moved around the bed until I was kneeling above her head. As I moved around her, I surveyed the arranged dildos and selected one that felt appropriate for the task - thinner than my own cock in its natural state, but perhaps marginally longer. I touched it briefly so that my cock would remodel accordingly, and then guided my firm shaft between her parted lips, noticing that now that the cock ring was within just a few centimetres of her neck, the glow from both was becoming quite insistent. Supporting the back of her neck with my hand to straighten her throat slightly, I found that I was able to slip my cock easily into her throat with no resistance, and could bury it deep until my balls pressed hard against her face. Needless to say, this is not something that I'd ever done to her before, primarily because she didn't want me to. But she had told me quite explicitly that when the collar was on, I had her eager consent to do to her all the things that she refused on other occasions. This was not a very long list, but what I was doing right now was definitely on it, and knowing that it was giving her pleasure allowed me to relax and enjoy it to the maximum possible extent. As before, the sensations when using this cock ring were amplified many times over, and within a few strokes I had that feeling as if I were about to cum; but it was an illusion, just an edge that I could ride for as long as I wanted to. I also realised that there was a kind of magnetic attraction between the two rings that tried to pull them closer. This force had previously been too subtle to notice, but as they were now so close together, it was too strong to be ignored.
I fucked her face hard and deep for a few minutes, enjoying the sight of her throat bulging with each thrust. Confident that she could take more, I allowed my hand to drift out to the side to briefly brush one of the larger dildos with a fingertip. Within a few seconds I could feel the additional tightness in her throat and see an even more impressive bulge. I could even feel the constriction of her collar. With this additional stimulation, my fervour grew, and one particularly aggressive thrust, combined with the strong attraction between the two rings, was enough to unexpectedly part her lips and force my testicles into her mouth. Similar to the first time I fucked her with the cock ring on, her lips immediately sealed onto the ring, and I was trapped. But now that I knew what to expect, I was able to relax and enjoy the ride. Her tongue and throat seemed to transform and get to work stimulating my cock and balls, and I was tipped over the edge. My orgasm was just as strong as when I'd used the ring before, but it felt like there was a much greater physical force behind it. Expecting it to subside after a few spurts of cum down her throat, I was somewhat surprised when it continued with sustained intensity, my body somehow producing copious amounts of semen to keep up with the demand. Jolt after jolt left my body, and soon I could see her belly start to bulge from the volume of liquid. Initially just a small swelling, it grew larger and larger, and the sight of it expanding and wobbling just made me cum harder and harder. The ability of her body to stretch to accommodate it was clearly not normal - the increased elasticity must have been another effect of using the two rings in combination.
Eventually my orgasm tapered off, and Katherine's mouth released its hold on my ring. My cock popped out of her mouth, with the ring still securely in place around the base. I panted while I caught my breath.
"Oh my little doll, you look amazing. You need to see yourself. You are the most wonderful sight to behold. Here, let me help you."
I moved around her, with the intention of picking her up and standing her in front of the mirror. As I lifted her upper body, I nearly threw her across the room by accident, because she was far lighter than I had been expecting. Raising her to her feet, I was able to tell that even with all that cum inside her, she only weighed about half of her usual weight. Once I'd positioned her in front of the mirror, I looked her up and down. Knowing that she could only stare straight ahead, I explained the sight for her.
"You can probably only see most of this in your peripheral vision, so let me tell you what I'm seeing. Your mouth is still gaping open, with a little trickle of my cum on your cheek. Your belly is swollen with an enormous amount of my cum, maybe five or six litres? Maybe more, I never was good at estimating. It's a huge round thing, it sticks out in front of your breasts," I said, giving her belly a quick squeeze to illustrate, "but still hangs a little over your waistband and wobbles about nicely. I've never seen anything so intensely sexy in my life."
I glanced down at my cock. It was still hard. And I still felt horny.
"I have to have you again."
Laying her gently back down on the edge of the bed, I spread her legs and planted her feet on the floor. I marvelled at the sight of her soft, enormous breasts and belly bouncing slightly as I put her on her back, rippling like the waves on the surface of a small pond. Her pussy had never looked as fuckable as it did right now. I lowered my head to give it a lick, initially a few gentle flicks on her clit, and then long slow tongue strokes that started with a little push on the butt plug and travelled the full length of her delicious labia to the very top. I inserted a finger in her pussy, then two, then three. Four was usually her limit, but today she felt more yielding, and my entire fist slipped inside her before I had realised it. Definitely not a loose fit, but also a much quicker and more effortless insertion than the one or two times that we'd managed it before.
"Well that's interesting, and confirms my theory. Using both of these rings has had a very noticeable and enjoyable effect on the elasticity of your body." I opened and closed my fist inside her, before gently sliding it back out. "So now I think you know exactly what I'm going to do."
I picked up the largest dildo and held it in front of her face with a filthy smile on my face, before tossing it casually aside. This one was a real beast, and stretched her to the absolute limit. It was the second largest dildo we'd ever owned - the previous record holder was purchased in a moment of naive optimism, and we had eventually thrown it away as she'd never been able to manage it. Lowering my hand to my cock, I found exactly what I'd expected to. It was now perfectly smooth and incredibly thick - not so thick that I was unable to wrap my fingers around it, but thick enough that when holding it I could only overlap my fingertips by a small amount. This would do the job very nicely. Normally when using this I'd have to take the butt plug out first, but with Katherine's current extra stretchiness, I was pretty sure that she could take both at the same time with ease.
I dropped a pillow on the floor for me to kneel on, and took up position between her legs. We had quite a low bed, which was very convenient for this particular position. The sensation of merely touching the tip of my cock to the entrance to her pussy, coupled with the sight of her enormous breasts and belly, and her face staring blankly at the ceiling with her mouth still agape, was sufficient to trigger the start of my orgasmic sensations. But the cock ring kept me on the very edge. Now that I was getting more attuned to the interaction between these two rings, I could more clearly feel the pulling sensation between the two, and so all I had to do was relax and allow my cock to be pulled achingly slowly into her pussy, millimetre by millimetre, until it was buried up to the hilt. I could feel a rigid unyielding bump pressing against the underside of my cock, which I knew must be the butt plug pushing through from its location in her ass. The pull continued, and I could already feel my balls starting to sink into her pussy, which was readily stretching to accommodate them. I knew that if I gave into this, the fun would be over too soon, and so I pulled back slightly to hold my cock steady and keep myself on the edge. With the additional length that this dildo had granted me, I could feel Katherine's insides in a way that I had not before, and realised that the tip of my cock was touching the indentation of her cervix.
"Words cannot describe how good this feels, my little doll. Your body just wants to pull me in, but I know what will happen after that, and I want to prolong this pleasure for a while longer yet. I want to see that liquid-filled belly wobble a little more, see how it ripples when I fuck you with everything I've got."
I withdrew my cock to nearly its full length. As I pulled back, the bump of the butt plug was dragged along the lower edge of my cock until I could feel it nestled into my frenulum. And then I started to fuck her with long, smooth strokes, being careful to gauge the right time to switch from pushing to pulling just before her body sucked me in entirely. With each stroke, her belly and breasts bounced in unison, a rolling wave of soft, pale flesh. As I became more comfortable with the necessary rhythm, I was able to pick up my pace, and the sight of her body moving in sync with my thrusting became more arousing with every stroke.
All of a sudden, and for no fathomable reason, the rings glowed much stronger, and the pull was increased too. Unable to alter my rhythm in time, I pushed a little too far, and the doll's cunt eagerly opened up to swallow up my balls and clamp to the ring behind them. I was trapped inside. At the other end of my cock, I could now feel the tight ring of her cervix locked in place around the bottom of my glans, meaning that the tip of my cock was now deep inside her in a place where it had never been before. With the cock ring's orgasm-preventing powers now deactivated, I immediately came deep inside her. Semen surged from my body in incredible amounts, and in just a couple of spurts the doll's womb was full and starting to bulge as more and more poured in. I yelled in delight, something between a laugh and a scream, as the sight of her body swelling once more spun my orgasm up to higher and higher intensity. Her belly now looked like a huge wobbling liquid pregnancy, sticking far up into the air. My orgasm waned, and stopped, and my cock was forcibly ejected from her pussy, with the cock ring still in its correct place behind my scrotum. A small dribble of cum leaked from her pussy, but it seemed like her cervix had closed back up and was containing the liquid within.