This is Muzan's wife, Rei and she has a daughter, Shiko. Rei was out usually cooking in their kitchen home and their daughter would just hang out around her father, Muzan Kibutsuji. Muzan I'd secretly the demon king and the strongest demon ever.

One day, Muzan was cursing himself and having a photo of his worst enemy when Shiko came in to hear her father cursing in his office. Shiko started to repeat everything Muzan with saying, even the curse words which shocked Muzan because he knew if Rei found out, He would get scolded. Little after, Shiko ran to her mother as if to say what she learned from Muzan. It was not long after in Rei came into Muzan's office.

"Care to explain why our daughter is cursing and saying she learnt it from you earlier?"

She glares at him, tilting her head as she waited for a response from her husband who sat there, attempting to come up with an excuse.