fth transformation

A female character undergoes a specific type of gender transformation which results in her becoming a herm (a female-bodied person with both a penis and a pussy). This type of gender transformation most often involves penis growth.

Not to be confused with

ftg_transformation - The female character's pussy disappears and is replaced with a penis, resulting in a gynomorph.
fth_crossgender - The female character is depicted as a herm without any transformation present in the post.