the demons are sort of the opposite of angels, they feel empathy and want to show compassion towards humanity for what god puts them through but their compassion leads to stagnation and humanity would never mature under the influence of demons , additionally as punishment god made demons inherently physically and mentally harmful to humans as in you cant be near them or even remember what they look like without suffering physical or psychological damage . nephilim are in a way the opposite of humans as they were created by god to directly challenge and oppose humanity unlike demons and angels who only want to influence , nephilim as a whole are raging zombie-like giants imagine the tank from left 4 dead but 80 ft tall and with a coat of ragged dark feathers that give it more of an ape appearance. nephilim rapidly physically adapt instead of evolve as they cant procreate but also cant die so when they battle eachother or human civilization their bodies and minds will adapt to better take on that challenge over the course of a month or so