Dantian

The spiritual heart, it is the core from which one channels energies through the meridians.

For a cultivator, it feels like it exists behind their navel, but it does not exist physically in a cultivator's body. Filling the dantian is required to awaken and begin production of one's own qi.

It is equivalent to the core of a beast, although spirit beasts being more tied to the physical, their cores are easier to remove. It is technically possible to harvest a cultivator's dantian as well "if you know the trick to it," but such actions are generally considered evil and has certain corruptive effects because a human's dantian is much more tied to their mind and soul.