Magic circuits.

Magic circuits are a pseudo-nervous system that spreads through the body and qualifies a person to use magic without consequence.

They are basically what connect people's body and soul and allow them to use magic. There are many ways to Activate Magic Circuits, Traumas, Training and hundreds of other hazards

The number of magical circuits a person has is defined at birth and can neither decrease nor increase. If the person's soul and body change, the magic circuits will also change, but the number of circuits will remain the same

Supernatural beings and humans who activate their magic circuits have an evolution in their bodies and their descendants inherit this same evolution and are already born with their active magic circuits

the energy, magic, Ki and any other that goes through the magic circuits can grow and make the person stronger, but there will always be the fact that those who have more magic circuits will always have an advantage in using this energy