Lua

The lua is a person's life energy.  This is the force within a person that causes their heart to pump and their breath to come.  A lua enters a person when they take their first breath outside the womb, and exits the body with its final breath upon death.  Unlike the other aspects of a soul, a lua cannot leave and wander on its own, because without it, the body immediately dies.
Every lua has a pre-determined number of breaths it can take. A person can still die before this limit is reached, but every lua will eventually run out of energy. The number of breaths a person can take is the ultimate cap on their lifetime.
The 'shape' of a lua defines the basic parameters of a person. The lua determines the range that a person's intelligence, creativity, determination, or other traits can fall in, and than a person's individual choices and decisions define what those actually are. For example, a person's lua might make them naturally talented at art, but it is up to the individual to choose to pursue that and put the talent to work, and a person without that inclination in the lua can still choose to take it up. They would just need to work harder.
You can capture a lua in a jar as it exits the body, and this is a powerful magical component.  Doing this is also deeply taboo, as an exiting lua should be returned to the air to eventually find its way to another person.