Willpower is an abstract measurement of one's own will to achieve a result. It is a separate resource from potentia, but like potentia it may be used to fuel magic. It is associated closely with will magic and consequently, users with stronger willpower will excel at will magic. However, burning it instead of potentia will cause injury. In most cases that are not life-threatening, its usage should be avoided.

There is anecdotal evidence to suggest that repeated burning of willpower within the safe limit may, over time, result in an increase in one's own willpower. However, as there is no means of measuring willpower (nor for that matter potentia), it is impossible to prove. Take this anecdote at your own risk.