So, because all of my ideas were semi-serious (and I really don't want to expend all of my serious) I decided I wanted to do something a little silly and humourous. I had an idea about how Drought Ninetales exist (pretty much just freaky Groudon sex) but I vetoed that one.
ONE HOUR LATER
I stumbled across a bizarre and curious pokémon anomaly (pokénomaly if you will) whilst thinking about random pokémon crap. It's the fact that Azurill is the only pokémon that has a chance of changing gender when it evolves. Expanding upon that, let's say scientists examine that particular quirk and find a way to adapt that irregularity for use with humans. Let's say it's one particular scientist. Let's say it's a scientist who has been known to test things on himself in the past.
Let's say Bill uses SCIENCE! to turn himself into a girl.