Karma.
It was the measure by which the heavens judged a cultivator.
Throughout the long life of an awakener, every action that affected the lives of other beings accumulated karma. If it caused agony and suffering to others, negative karma was accrued; if it brought relief and happiness, the karma accumulated was positive.
Negative karma reduced the chances of breaking through to higher realms, while positive karma provided greater opportunities for advancement. If a cultivator killed another cultivator with negative karma, they would gain positive karma; the reverse was also true if they killed someone with positive karma.
Before the Second Ultimate War, Taranis had slain thousands of demons in the Sentinel Line and cultivators in the Abandoned Lands, all of whom bore heavy negative karma. His actions accumulated a vast amount of positive karma, allowing him to ascend realms with relative ease.
