Jack’s best mate, Charlie, has always been effortlessly cool. When Charlie wakes up one day and finds a mysterious, moving black tattoo on his back, it’s a clear sign that he’s even cooler than Jack thought. To top it off, Charlie is suddenly able to fight like a kung-fu master, fly, and control the minds of others. Yes, he’s got super powers.
Or does he?
Jack soon learns the terrifying truth: Charlie’s incredible powers come from an age-old demon called the Scourge, who is using Charlie to bring about its evil master plan. To stop the Scourge, Jack and Charlie join forces with Esme, a girl with super powers of her own, trained from birth to fight the demon. But time is running out, as Charlie falls deeper under the Scourge’s dark spell.
When the Scourge vanishes with Charlie, Jack and Esme follow their friend from the streets of London into Hell itself, where they face horrors that may well cost them their lives. Can they survive to outwit the Scourge, save Charlie, and stop an even greater evil?
It was really weird; the tattoo started on one character (I'm thinking it was a female character, but I really don't know) but then became sentient and lived its own merry little life, and I think ended up screwing at least one of the female characters?
Esme is the daughter of Felix who when Esme was conceived was possessed by The Scourge, though this is not originally known. Esme thought her father was Raymond, but on the night she was conceived Felix had magically transformed to look like Raymond in order to get one night of happiness with Esme's mother. She trained her entire life to fight the Scourge, and is extraordinarily talented in the martial arts, flying, and art.
Wikipedia, The Black Tattoo
This review on Goodreads also mentions at what you could be thinking of about it moving bodies and someone having sex with someone else.
See, for the past thousand or so years, the Scourge, defeated and imprisoned by a powerful curse, has been watched over by the Brotherhood, one of those super-cool, super-secret societies. (They're not totally cool, though, because the Brotherhood lacks the dramatic costumes and complicated secret handshakes. Shame on them, the slackers.) Now we come to the tricky part. One of the Brotherhood defects the order, frees the Scourge and lets himself be possessed by the demon...to win the affections of a girl, naturally. The treachery is discovered, a war is fought, and the Scourge is once again defeated, or so the Brotherhood believes. Truth is, the Scourge is still free and waiting for the perfect vessel to take over, a nicely gullible, angry, malleable vessel, so that the Scourge can put his plan in action. Little sullen Charlie is the perfect fit.
Goodreads, The Black Tattoo, Lolly's Library's Review
It was a sci-fi book with a red and orange cover on the hardcover edition.
