original theory: succubi are always women, incubi are always men
facts: in fact succubus comes from the latin word “succubare” which means “to lie under” and incubus comes from the latin word “incubare” which means “to lie on”
new improved theory: incubi are always tops and succubi are always bottoms. gender doesn’t matter at all.
addendum: if the sex demon in question is versatile, they’re a concubus, from the latin for ‘to lie with/beside’.
Lyn'to's Sanctuary 