That's Not What Rule 63 Is Either.

The guy in front is also the girl in the back

To answer that question, I couldn't come up with a feasible answer. The way I'd put it, Rule 63 was a joke rule that, like Rule 34, is seemingly taken seriously by the internet, as the genberbends are about as numerous as the NSFW and pornographic pictures out there.

With Ranma here, the lore had it to where Ranma's sex change is a curse brought unto him.

He definitely is an exception to the rule. I've seen a lot of things on the internet that I cannot now unsee. I have seen Wonder Woman using her Willy to cornhole Superman, get cryin' out loud.

Not my fetish, but shit I see looking for other shit. No shit.

I have the first four seasons of the series and just ordered season 5 last night.

He was knocked into a cursed look by his father, who had just gotten out of one Ranma had knocked him into. The curse is that if you fall in one of the cursed pools, you assume the shape of the last thing that drowned in it. Ranma fell into the pool of the drowned girl, his dad into the pool of the drowned panda.

This is def the exception to the rule, especially as it is canon in both the manga and anime. All other gender bender is non-canon, with the possible exception of Superboy who had an illusion that he was a girl in a story back in the 50s.

This is a part two to this meme: imgflip.com/i/1lkaoz