If you know One Piece, it's practically like Conqueror's Haki, but it can manifest physically. Basically it's like a gut-wrenching fear that you feel when you see a dangerous, one-step-and-you-are-dead animal. Take that fear and make it physical so that even the air itself is full of fear for a beast so much you will have trouble breathing and moving. And that's a Beast's Fang. It's even more powerful than aura and mana (or is it magic) in this universe, probably because it's hard to ignore your instinct as a living being.
So far, from what we know:
1. Only MC's bloodline can manifest it, so it's definitely hereditary, though I think not every descendants can have it.
2. Only a Beast's Fang can counter another Beast's Fang.
3. Using a Beast's Fang takes toll on you physically and mentally, so you actually need to be strong to use it.
4. Kids are more prone to losing control since they're still young, though I assume that if you're compromised mentally, as an adult, you might lose control too.
If you read this far, know that these are all just my assumptions from what I read of the manhwa LoL. If I'm wrong feel free to correct me.
Bro can someone explain what the beast fang even is? Maybe i missed the description of it somewhere but all i see is them getting angry and everyone just falls down to the ground. Like is it an elemental power? Psychological? Someone pls explain what it actually does to the human body ( ̄∇ ̄")