The old woman's disease is known as the Heart-Eroding Soul-Snatching Disease! For many, it is certainly tricky, but for him, it was merely a bit of a hassle.
This disease is extremely rare because those who contract it are usually bitten by a creature called the Heart-Eroding Soul-Snatching snake.
The Heart-Eroding Soul-Snatching snake is very rare, and some even say it's extinct. This snake has no poison or taste, good at changing color and hiding, but its body harbors a potent toxin!
Crucially, it is especially lethal to those with a body refined for cultivation!
The stronger the individual, the stronger the poison!
Fortunately, this girl's grandmother was not a cultivator, otherwise, she would have met Yama long ago.
But this snake has been extinct for a thousand years, and the old woman was presumably bitten two years ago, which was one of the reasons why Ren Feifan found the disease so odd.