Part of an universe. Woman demons appear, fall in love with human men. 1st few of the stories in the universe are between a pre-puberty girl demon, her male lover and the boy's crush cum eventual lover girl. Coming of age for the trio. IIRC the demon was purple/blue in color. Last story I read brings a new "man" who survives a car crash/accident and meets red demon lover. By that time the trio lovers were in their twenties.