Gender flip

Gender flip or gender swap refers to stories in which a character of one gender undergoes some kind of sex change at some point throughout or before the fic. They are usually sudden and unexpected, caused by magic or alien technology. They can be temporary or permanent and irreversible. They can be serious or, often, quite humourous. They may also indicate stories in which a character who is canonically one gender is and always has been the opposite gender within the fic, such as a canon male character being rewritten as a female in 'always-a-girl' fics.