Vigor (기력, gi-lyeog) determines the amount and strength of spells (in the case of pure-bloods and quarters) or transcendentals that a being can use.
Pure-blood humans typically have very low maximum vigor values but relatively high recovery rates. They can recover vigor by either eating or sleeping, and their vigor recovers faster if they are happy.[1] In comparison to pure-blood humans, halfs tend to have higher maximum vigor values. Eating meat is the most efficient way of recovering vigor for halfs. Quarters have characteristics in between those of pure-bloods and halfs.
Gods and suras have a much higher maximum vigor value compared to humans. Gods and nastikas recover vigor over time based on the type of environment that they are in, while lower classes of suras must eat in order to recover their vigor. However, fifth-stage rakshasas are able to recover vigor without eating, like nastikas.[2]
Dragon halfs can use vigor for spells if over 100 years old.