Sun Yan cultivated a Demon Sect technique called the Poison Fire Demon Art.
The technique was extremely powerful and imbued with a potent fire poison that was astonishingly lethal.
However, it suffered from a hidden danger, the fire poison backlash, which would cause psychological damage.
With Sun Yan's perfection-stage cultivation, it was already evident that the higher one cultivated the Poison Fire Demon Art, the higher the chance of the backlash.
With his mental cultivation, he could vaguely sense that he absolutely should not break through to the next level. But even if his cultivation remained stagnant, he would still gradually suffer the demon art's backlash!
The only ways to help him were either finding a rare treasure or having someone at his cultivation level fill him with cold attribute cultivation power to suppress the demon art.
The thousand-year Cold Heart Vine was one such treasure.