@Tcof It depends on what legend/story you read actually. Some say the victims would only lose their energy, but some say they would die because their energy is all sucked out so yeah. In this case I think it's the latter
@Tcof@Yatsuki Various sources do vary vastly... Including those that deem succubus just female form of devil that f8s you as consolation for selling your soul after the fact.
Generally, "only little bit of energy" is mostly indulgence of manga, otherwise making any kind of deals with devils cost you highly.
Wait, I can put it more simply:
Succubus is a cautionary tale against thinking with your dick, not about ways to have sex without consequences.