Sometimes scars are more sensible than the normal skin but it depends on the type of cicatrization (づ￣ ³￣)づ Tho I find that the explanation goes more for the kinky one as far as I've read in the novel
Scars can be a bit sensitive sometimes. I have a scar from my appendicitis that is sensitive compare to normal skin. The result is that it is extremely itchy. Slight touch makes me wanna scratch like crazy and it's been 5 years now. For renato case, it's a sexual thing.
However, in the novel, something the manhwa sort of left out, is that Renato was never aroused when the scar was touched. It instead caused him to be in pain. The scar was painful and it was a painful memory. It was khalid who made the scar into an arousal. His touches along with his foreplay is what made it to be a pleasurable spot.
Why does the scar make him horny