>>1417yes, everyone knows functionally she's some kind of succubus. But what kind? Is she a European succubus or is she from Japanese folklore? The series never identifies her. The issue is that everyone else is clearly something: Lum is an Oni, and Benten is the Shichifukujin Benzaiten. Oyuki is a Yuki on'na.
Then that leaves Ran who is… something? Something magical? Given the theming she should be part of Japanese folklore as well, but she's too vague to fit anything and the series never identifies it. Fans have tried to figure it out for 40 years.