Finding Your True Love (Demon Slayers x Oc)

10 years ago, rose used to be happy child, helpful and save people from danger. but on her 10th birthday and return from the hospital after she saved a teenage girl named Roxana love from getting hit by a flower truck and Roxana's stepmother was arrested for attempted murder on her own stepdaughter by Roxana's father and the polices. Upon return to her mansion and saw the servants and her family were killed by demons and Muzan the demon king and tried to kill her best friend luna. She make a deal with Muzan if he promised no to hurt and spare her friend and her pet cat Grim to stay with him forever and he agreed to it. The biwa demon stuck the strings and seperate them and promised to be reunited as friends forever. During her imprison in demon fortress and Grim to keep her company, she was forced to be his bride. Will she be safe from Muzan and his demons or fall into darkness?