Hey everyone, I am breaking my head all weekend for some creative ideas on this topic and I came up only with a few ideas. The defining element should be some sort of mental/physical transformation. Classical that could be a bimbo transformation, but I was also thinking about dolls or sex toys or a girl having an urge to be bred or she suddenly becomes super flexible (imagine for example a girl tied up in a knot). It either could be some couple or someone messing around with a larger group. One idea I had was some sort of computer virus, which twists tech in sexual ways or causes chaos by it. Imagine it infecting the speaker system of a mall or maybe that of a gym and suddenly everyone getting mad at fucking each other. Maybe someone has a thought either on this idea or on the whole setting in itself.
I like the Special Sound That Makes Everyone Do <Fetish> idea a lot. It lends itself well to causing the kind of Everyone Goes Crazy For Sex dynamic you seem to be going for, because it'd affect lots of people at the same time. Building on it: you could do something with binaural beats. The supposed benefits are total bullshit IRL, but in a fictional story you're not bound to the limits of known science. Something else you could borrow from is ASMR. If you'd like your protagonist to remain wholly or partly in control, they could be the person to discover/invent the Special Sound (during a school experiment?), or be uniquely immune to it (because of a recent accident?). Later developments could wrest that control from them, providing conflict. One downside of using sound as your trigger is that I'm having a hard time coming up with a mechanism for how that would cause physical changes in people, which also seems to be something you're aiming for. I'm not sure how to combine those two interests without sharply deviating from your original idea (for example by going the sexy global pandemic/sexy zombie apocalypse route).
