I didn't write this but I have been given permission to post this all credit goes to Valentinesdaygreen and a link below to the original story origin http://valentinesdaygreen.deviantart.com/

Slenderman found (Y/N) as a baby and raised her. She's younger than the CreepyPasta's being about 6 years younger than all of them (except slender of course). When her 15th birthday comes she gets a present she wasn't quite expecting.