I understand libertarian free will as an agent's ability to choose otherwise, or having more than one course of action available to them, when making a choice at time t, given a fixed past up to t. However, after having partaken in multiple discussions related to the concept of free will on the Christianity site (for the curious, see here, here, here, here), I've noticed that the concept of character is very important for at least some proponents of libertarian freedom. To illustrate this, let me quote this answer:
The "missing link" here is character. God has free will, and is fully capable of being tempted and enticed to do evil, but consistently chooses to use that free will in benevolent and righteous ways.
Or this answer:
Christians have free-will, but their purpose in life is to develop perfect characters that always freely choose not to sin. They can develop this God-like character, but by definition no one can be created with it.
Yet, I still have to understand what character is in the first place. Is there a rigorous definition of character? Does character exist as a "thing" in the first place (i.e., what is the ontological status of character)? Does character have any measurable or detectable causal effects on reality? For example, does an agent's character influence said agent in a way that determines or narrows the range of options available to them at time t, and if so, how?
And what is the relationship between an agent's character and the laws of physics? Is character nothing but an emergent property of the laws of physics, in the sense that the concept of character is a convenient high-level abstraction, but ultimately adds nothing new to what the laws of physics can already explain? Is a person's character nothing but the current state of the neural wiring of their brain? Is character nothing but brain chemistry? Or is character something beyond the laws of physics, not reducible to them, and different from free will at the same time?
And if character goes beyond the laws of physics, where is the information of this character stored? Can it change/be updated over time? Does it obey its own "character update rules"?
In short, what is character, and what role does it play in the decision making of an agent, according to proponents of libertarian free will?
Regarding my sub-question about the relationship between character and the laws of physics, this question is closely related: How do defenders of libertarian freewill reconcile it with constraints imposed by the laws of physics?