addendums: cult classic tv overlaps with early supernatural seasons somewhat, i am aware, just choose based on the cultural context in which you read your first fic.
for weeaboo crew i was thinking of examples like hetalia, black butler, soul eater, etc--popular anime absolutely included but the distinction is that people who were into dragon ball weren't necessarily going to anime club every week and making deviantart stamps about yaoi, but people into ouran high school host club ABSOLUTELY were.
homestuck is in its own category because homestuck changed fandom forever at a critical time which just happened to be when i was growing up in fandom. harry potter, lotr, star wars, and twilight are in their own categories because they were such multimedia juggernauts they had entire archives dedicated solely and only to their fic that spanned multiple franchise reboots (books -> movies -> extended universes). (i acknowledge star trek technically would fit under this but at the time culturally it had more overlap with other cult classic tv fandoms.)
honorable mentions that didn't make it to the list because i had to pick-and-choose with the 12 answer limit: the final fantasy franchise (axed because i am not familiar enough with the fic scene to know if it was as iconic of a gateway drug as, like, naruto or twilight or star wars fic), a general YA lit category (YA lit outside of twilight only went mainstream slightly after this time period), the MCU (i have a hate boner for the MCU), a broader "american superhero comics" category (this would be valid as an option but i don't have the space)
