Tokusatsu said: There's a difference. Demon girls are just demon girls while succubi are nymphomaniac demon girls. There's a difference, however small it is.
Plus the succubus myth says, that they feed from the soul of their victims, while demon girls could just be anything.
hungkok2007 said: Yes, but we are looking for the visually discernible differences as apply to Danbooru. Or deciding on appropriate terminology rules.
Demon girls are visually obvious as being demon girls, but a succubus is defined in part by behavior as well. So I wonder if maybe that tag should only apply where a character's known to be one since context is part of the definition.