Usually, a Beast Core could only be formed in the body of a powerful fierce beast or a Demon Beast.
However, usually, only a fierce beast or the Demon beast who stood at the summit of the Cloud Continent, which was also known as the Demon Emperor, could have left a Beast Core behind upon its death.
Everyone knew that once a fierce beast broke through to the Void Prying Stage, it would undergo a transformation to become a Demon Beast.
The moment the fierce beast transformed into a Demon Beast, the Beast Core in his body would form a tight bond with its body's energy that could also be referred to as a symbiotic relationship.
If one did not make a breakthrough to the Martial Emperor Stage, this symbiotic relationship would not be able to be called off.
For this reason, even if an ordinary Demon beast was killed, it would not leave behind a Beast Core because at that very second, the Beast Core would be shattered along with the dissipation of its energy.