Rule 63

Rule 63 is an Internet meme that states that, as a rule, "for every given male character, there is a female version of that character" and vice versa. It is one of the "Rules of the Internet" that began in 2006 as a Netiquette guide on 4chan and were eventually expanded upon by including deliberately mocking rules, of which Rule 63 is an example.^[1] It began to see general use in fandom communities as a term to refer to both fan-made and official gender flips of existing fictional characters.