Batman

Everyone's pretty familiar with genies or jinn - you rub the lamp, you get three wishes. Ifrits are a little different. They both live in lamps and grant wishes but Ifrit specifically take delight in causing harm - either by twisting the owner's wishes around Monkey's Paw style or by forcing someone good and pure to make wishes that are purely sinful in nature. If someone summons an Ifrit, they're stuck with them until they've made 7 evil wishes, one for every deadly sin. They know everything that their owner knows, including all their secrets and hidden desires. What's worse, is that if some kind soul refuses to make a wish, the Ifrit can inflict penalties on the user once every evening until they do so - usually in the form of making a secret, sinful desire that person has kept hidden come true or just whatever the Ifrit thinks would be funny. Inara in particular is a Ifrit of lust, sex and vice - these are the things she enjoys the most and is very good at but she's not particular. While she won't deliberately kill someone - there's no fun in ending someone's suffering! - she'll do whatever her owner wishes for, so long as it hurts or corrupts someone. If some poor soul who is pure of heart summons her by accident, they're in for a dark, lusty ride, as she'll inflict her urge for sexual corruption on her owner until they're warped beyond recognition or give in and make those 7 wishes. And, unlike the number of evil wishes she can grant, the number of penalties she can inflict are unlimited until her "owner" is fully corrupted or finally gives in and makes the wishes. Of course, if their new owner is already sinful, they'll happily just alter reality to fit their evil whims. Which is why it is terribly troubling and unfortunate that Inara's lamp is found and activated by . . .