Five Secret Family.
Hera once heard about this legendary family as a kid. Back then, Vicenzo, her father, found his interest in this secret society that the Five Secret Family was leading. Vincenzo's reasons when she asked why, were simply to sate his curiosity.
But it seemed her father wasn't simply sating his curiosity.
Old Madam Zhu didn't know too much about the Five Secret Family besides the crumbs Felice told her. According to her, these Five Secret Families were so powerful they had control in many regions of the world. They could incite war and put the whole world in chaos with the flick of their hands. They could even kill a country's economy if they so pleased.
Just that alone was enough to bring fear to anyone. Hence, the many big nations kept their existence a secret. The mere idea in fiction was enough to make people wonder and tremble in fear, but if people knew this was actually the reality, it could mean a lot of things.