Hello fellow demon, Shima here is going to be a hellfire-based demon, so... kind of the opposite of Elsa. Even so, maybe they have some kind of CR?

It could be just about anything, even negative, since the funny part is, Shima has all his memories and therefore no idea how they know each other. It could be really ridiculous or really, really dangerous.

edit: And then I fleshed out more on Shima's demon background in his own comment elsewhere. He's now also That Demon That Owns a Stereotypical Supernatural Nightclub, so it could be as simple as "Elsa just hangs out in the VIP 'leave me alone' section and chills her own drinks".