Plaqueus

Plaqueus is a disease god that Malamaya was friends with, and she was more than happy to ask him to craft her a genetic time bomb that alters their DNA and randomly infects people. Once released, the disease was shared everywhere on the surface, engraining itself in DNA so that humans going past 18 would transform into a pregnant women about to give birth unless they were destined to be a very desirable dude, saving the uglies from hardship later on in life.

But since that was only half the disease, the other half kicks in randomly for bros across all ages, transforming dudes into chicks and chicks into futas or men with very dominant and attractive builds for those desiring the ultra-masculine vibe without the doucheness accompanying cocky guys born big.