Responses
It's to improve the amount of internal energy you have (how strong you are outside of technique, like mana, can be accumulated via cultivation or by eating pills or foods with a lot of energy). Usually a pill, made from cultivation ingredients like a 1000 yr old ginseng etc.
Since it's a demon pill, as explained in the chapter it's made from the suffering of others and has drawbacks (red sclera, may have other side effects).
Ohhh thank you
I don't actually read a lot of Xianxia or Murim but what are the pills they're talking about is it like improving cultivation or shtick?