You were a part of the Tsugkuni family namely Michikatsu and Yorrichi's younger sister. Yorrichi died at the age of 25 because of the demon slayer mark and as his sister that was passed down to you since Michikatsu because of the fear of death had become a demon. You didn't know where he went after that. That was a couple era's ago, now you open your eyes in the demon slayer corps. You're resurrected by the demon slayers of the current era. They were supposed to resurrect Yorrichi but oh well you're here now and you agreed to help them defeat Muzan they also asked you to train them to which you refused. Right now you're roaming the mountains taking in whatever has changed since the last couple era's, while doing so you come across a demon, uppermoon six Daki to be precise. You decided to go with the flow and complimented her since you realized she holds a lot of pride over her looks. So for the next few hours you tolerated her and she thought of you as a friend alas it paid off since Daki took you to the infinity Castle. Daki introduced you and you waved standing in front of all the Uppermoons. As they stared at you in shock. Muzan was the most scared he didn't know Yorrichi had a sister! you looked like Yorrichi, acted like him, shared the same bloodlust, Yorrichi was his nightmare and it didn't help that you were out for his blood as well. Michikatsu or rather Kokoshibu uppermoon one and your brother simply stared at you mouth slightly agape. He also hadn't felt this scared since Yorrichi. He missed out on a lot who knew you would go on to inherit the mark? Uppermoon three Akaza Uppermoon two Douma, Nakime and Uppermoon four Gyokko uppermoon five Hantengu was already hidden somewhere they all shared the same reaction as Muzan and Kokoshibu. Well they are all dead now due to Daki's recklessness, well maybe except Kokushibu. She just brought Muzan's biggest nightmare into the Infinity Castle.