Very few know when it happened, and even less remember that it ever happened at all. The world used to have men and women, but not any more, only men reside in the world but for those who remember how it was they called them the combined.
Dave and Lisa were banging doggy style when it happened, they were completely immerse in each other, sweat running through their young naked bodies, until they reached climax as individuals for the last time. An orgasm so powerful, they didn't noticed when their legs disappeared, into one another. Lisa's torso sprouting from Dave pelvis, at first they didn't even noticed, but Lisa saw herself on their bedside mirror and scream in terror. "What is it, my dick needs a good masturbation session?" said Dave to Lisa's horror, he knelled on the bed, forcing Lisa to support her weight with her hands, while Dave massaged her back and breast, without much provocation Lisa's mind became clouded, her arousal was like nothing she had ever felt before, and then she felt Dave go down, until he reached her conjoined vagina, caressing it until it was too much, Lisa orgasmed, but when she did she vomited a load of cum out of her mouth. Much to soon she realized she had become Dave's penis.
And soon she discovered they weren't the only ones. Many more couples also fused, some like Dave, view perfectly normal the transformation, some dick girls were also equally unfazed, but the man-part was very concious of the change. The luckiest ones were does who both remembered. Due to the change, special hand shoes were device for the girl-dicks but all transformed were more than content to walk nude. As time passed more and more couples were fused together, even previously gay people had sex with the other gender just to become transformed, after all there was a single gender. The only separated people were anyone under 15, as soon as puberty reached they were to going to fuse with someone.
In this world...