y/n kibutsuji was muzans little sister who suffered from the same disease he did. they first met when she was 5. Listen i have read a lot of amazing story like this but they never have the ending im looking for. or the excitement im looking for that comes with siblings. I have siblings of my own. and scenes im the oldest i can best incorporate this the way i like. and i hope you like it too I do not own kny all credits go to the creator. I only own half of this plot.