[[WMG: The Cloak Invisible is a Cloak of [[ByTheEyesOfTheBlind Invisibility To Virgins]].]]
The two people on whom it worked, of a group of vikings and a group of hedonistic people, were the Christian missionary and Aud's "father". Most sects of Christianity prefer that their clergy not have sex, and usually make it a requirement, so that covers Harald. As for King Arnulf, he is a very naive and gullible married man whose wife had a cloak of invisibility that worked only on him, and if the guess is correct, it would cease to work on him if he ever lost his virginity. Think about it.
[[WMG: Aud is the same Aud from Series/BuffyTheVampireSlayer]]
Viking, dark hair, marries an easy going guy, and has a rather relaxed attitude towards sex? She's clearly the same Aud who is to become Anyanka the Vengence Demon. Plus, [[RuleOfCool it would be awesome.]]