Before the Great Fusion Wave, Kentonville could have been Anywhere, USA. However, the Great Fusion Wave, or GFW for short, was not kind to the city. For a currently unknown reason, the GFW hit Kentonville much, much harder than most other parts of the world. Every single person in city limits transformed. Even more bizarrely, the GFW fused the entire town in the exact same way - as each (not yet fused) person got hit by the GFW, they would be teleported to the next physically closest person to them and become their lower half. The new lower halves would have their head mounted on their host's crotch and the lower halves' legs would replace the legs of the host. Each half would feel the whole body, but could only control their half.
Additionally, the upper half's genitals did not disappear. If the upper half was a woman, the lower half's mouth would take on some qualities of a pussy - the tip of the tongue would become as sensitive as a clit, there would be a G-spot on the roof of their mouth, and drooling would kick into overdrive when either half gets aroused.
If the upper half was a man, the lower half would have the upper half's penis and testicles embedded deep at the back of their mouth. While the dick could be easily ignored when flaccid, when either half gets aroused, the penis both becomes erect and moves forward in the lower half's mouth. The lower half would be left with balls pressing against their tongue and the cock protruding proudly from their mouth, freed from its sheath.
Residents of Kentonville struggled heavily with the changes. People who were 'lucky' to become an upper half, colloquially known as tops, tried to figure out not only how to live with a 'bottom' fused to them forever and how they could continue their normal life, but how to make their bottom's life more tolerable. Male tops, particularly those with high sex drives or thicker members, struggled even more with the final point. Bottoms struggled further, with those from out of town often not recognizing them as a person - only a head hanging off an actual person's body. Tensions, understandably, ran hot.
The mayor of Kentonville, Monica Trey, had been hosting her daughter Jess on a visit back from college. Unfortunately, Monica had taken the right side of the couch while Jess sat on the left. Monica got hit by the fusion wave first, causing her to get fused to her daughter's lower half. Monica's head burst through her daughter's skinny jeans, and Monica's thick thighs and ass caused Jess's jeans to finish pulling themselves apart. After the pair panicked and turned on the news, both minds started panicking about their new situation. How could Jess go back to college? How could Monica run the city from between her daughter's thighs? How can they be in two places at once? ... Do mother and daughter have to share a sex life now?
Another two victims of the wave were John and Kelly, two office workers at a local company. Both were married, but not to each other. Despite that, they made up stories of long and hard overtime to tell their spouses and stayed after-hours to continue their affair. The cheaters got hit by the Great Fusion Wave mid-thrust, with Kelly getting hit first, adding her head and womanly hips to John's anatomy. John screamed and Kelly tried, but she already had his thick, long, erect penis sprouting from her mouth. Her favorite part of him quickly turned into her nightmare. John and Kelly had to figure out their excuse for getting fused - the bosses had no idea they were staying this late, and they should have been on opposite sides of town at this hour...
Two film students and roommates, Alex and Alexis, had been drinking and watching old, crappy movies together, laughing at all the awful and nonsensical elements of the movies. While watching, Alex got hit by the wave, getting himself fused to Alexis, his head and hairy legs replacing her lower half. The pair started screaming in panic, followed quickly by screams from others in the dorm. They had lived together for a few months and liked each other well enough, but sharing a body is a lot more commitment than sharing a room.
The entire town got hit by the wave, and while panic ripped through the town initially, the town pulled together to try to forge new lives together.