Your girlfriend dropped to her knees and took your massive dolphin cock in her mouth. It felt so good to have her run her tongue all over your sensitive appendage. You didn't think was possible, but somehow you became even more erect. Despite your earlier jerking off you were desperate for release. Your heard your girlfriend briefly gag as she tried to take you too deeply in her mouth. She'd given you head many times before, but never gagged from your normal penis.
She took you out of her mouth and sighed with obvious disappointment. "I don't know if I can do it. I want to, but it's so big."
Somehow, you know the way. "Can you at least finish me off?" you ask innocently.
She nods and begins to suck your dick again. The pleasure and pressure are mounting within you. Normally, you'd warn her. Not now; not if you are going to mate with her.
She has you about as deep in her mouth as she can go without gagging when feel yourself begin to quiver. You grab her head with both your hands and explode. You hear a muffled scream as the semen floods her mouth and goes down her throat. It only takes a moment then you're done and release her.
Your girlfriend falls backwards onto her butt, coughing and gagging from suddenly ingesting a big gulp of your precious bodily fluids. She's never swallowed you before. She kicks you hard, fortunately only in your shin and not somewhere more sensitive.
"Why did you do that?!" she yells.
"It was the only way" you say.
She glares at you as she waits to regain her regular breathing. She's mad at your little stunt and as much as she wants your big cock in her now she's having second thoughts. That's when she realizes despite blowing a load your big gray dolphin penis is still massively erect. How? She stumbles to her feet to walk away, but she realizes she can't help but stare at it. She also realizes she's wet. Very wet. Wetter than she's ever been before. Juices start to run down her leg.
Somehow she knows she can make it fit now. She climbs onto you.
"How did you know?" she asks.
"Instinct" is the only explanation you have.
She guides you into her. Pushing you into her. Slowly. Carefully. As good as the oral sex was, this is what your penis really wants: her warm, wet walls tightly around it. She stops for a few deep breaths, backs off a little, then pushes you deeper. As she's sliding you into her the two of you kiss, hungrily, animalistic. She gets you about as deep as it seems possible then starts to back off. When you're only about halfway in instinct takes hold again. You grab her ass cheeks and slam her onto you, deeper than she thought possible. She cries out in a mix of pain and pleasure then begins to orgasm. You climax for the third time, more than either time before. You pump you seed deep in your mate, holding her tight against you. You filled one part of her with your fluids; now you fill another.
When you are finally finished and let go of her she slumps exhausted against you. For the first time since your anatomy transformed after drinking the pond's water you feel yourself soften.