it's more like a hereditary genetic disorder. If one or both your parents have it you can have it too. As at least that's how I understood it.
http://www.mangago.me/read-manga/devils_line/nbt/manga/devils_line/c042/pg-11/
I think this chapter is the best they explained it. I could be wrong there might be a better explanation on earlier chapters
Personally, I think that evil are just vampires no ?
Thanks though the current chapters answered my question directly. HAHA. Apologies for asking without reading the chapters first.
No need for apologies
Guys can anyone direct me to the chapters that explain the devils? Or give a summary? Sorry, I just forgot what they are. Are they a separate race or humans infected with vampire blood/genes/virus? Thanks.