As anyone who has played Touhou will tell you, the boss fights are what these games are all about. There are well over 100 boss characters in the series, and you encounter most of them only once, so it's natural that some make a more lasting impression than others. In Fanon, they might be famous for their colorful personalities, ridiculous cuteness levels, or Memetic Sex God/Molester status, but for those who have actually played the games, they will always be fondly remembered for a different reason.