Here are some possibilities:
* "Fore-fleshing" might be a typo for "foreshadowing": This refers to hints or clues given in a story or other work of art that suggest what will happen in the future.
* "Fore-fleshing" might be a deliberate neologism: Someone might have created this word to refer to something specific in their own work or context. Without further information, it's impossible to know what they intended.
If you could provide more context about where you encountered this word, I might be able to offer a more specific answer.