The reason that Marcy has light red skin and Delilah has red skin isn’t cause they are demons (far from it, they are not demons) but cause Kokoro skin change color as they get older, when they are 1-12 years old their skin is pink, 13-18 light red, 19-28 red, 29-39 dark red. Once they turn 40 their skin color changes to a reddish purple, and their horns fall out the same way that human baby teeth do.