Vampire Diaries
Details This is a challenge not a story. just making that clear now.
Instead of Stefan finding Katherine's suicide letter, Elena finds it and saves Katherine instead. This sparks the sliw bonding between the two enemues. They'll go from enemies to frienemies to friends to lovers at a relatively slow pace -mostly. And certain things must happen, such as them discovering that despite vampire blood not supposed to be able to help Katherine - Elena's does. Simply, because she is a doubleganger and dopplegangers have special connections with each other. Whether you wish to turn Katherine back into a Vampire using that connection or not or into something else entirely is up to you. But if you turn her back into a Vamp, she won't start off as a newborn. She'll return to exactly how she was before she turned human.
Must be Rated M. And the pairing is obviously Elena x Katherine. Best of luck to whoever decides to take my chalkenge and pm me if you wwant it.