Heroic Heretics are heroes who oppose a major religion or deity worshiped by the mainstream populous of their society. They oppose not merely isolated harmful cults and forgotten gods of long ago but full-blown religions and pantheons. This is most often done when the heroes in question are facing corrupt religious leaders but may even extend to the deities of the mainstream religion. A rarer form of this is when the hero is not outright opposing a religion but rather has done something considered blasphemous by mainstream religion, such as breaking some form of tabu, like entering forbidden grounds or practicing magic that is considered to be unholy. This may even extend to less outrageous but still technically heretical practices such as women in the middle-ages who learn to read.
This is often opposed to Religious Heroes, but not always, as some heroes may be considered heretics even while still believing in their respective religions, such as Yuna or Scar.