Gibbs is a vampire. Emily is an NCIS agent in his team. Emily is a witch. Vampires need blood, around one liter a week. Humans can only give around two pints, or one liter every 6 weeks. Because of this, human blood is hard to come by. It has to be willingly given and you have to do a ton of tests and everything. Witches can give the same amount of blood, but they replenish a bit quicker. Witches donate the most blood. Witches also have covens, many covens have rules about donating because for hundreds of years vampires and witches have had contracts. Basically, if witches give blood, vampires don’t drain witches. Gibbs and Emily get along well. Not everyone knows he’s a vampire just bc he naturally hides it well. Emily is an Electric witch and a divination witch. Emily knows Gibbs is a vampire and Gibbs knows she’s a witch. Witch’s blood smells different than human, and usually is more sought after by vampires.