The year is 2025 in a slightly alternate universe. I'm 1996 science created pills that could completely change someone's sex. Over the years these pills have become commonplace, and advanced to the point where almost anyone above eighteen can take them if a doctor prescribed them.
These pills will completely change your sex in only eight days, with the transformation happening gradually over each day as the pills tale effect. They also have variations, and mix and matches. Someone can become entirely sexless, become a masculine woman or feminine man, have a genital setup that doesn't match their body, or have a mix of sex characteristics, or even how high or low your libido is. The only drawback is that once you've completed the transformation you can't safley transform again for a year.