You were Muichiro and Yuichiro’s older sibling. The best in fact. You took care of them after your parents died.

Though, the night the demon attacked, you were nowhere to be seen, you were presumed dead. After the demon had hurt Yuichiro by slicing off his arm, Muichiro killed it. Soon after, Yuichiro died due to blood loss. Muichiro never found you and developed amnesia from the trauma. They were 11 and you were 13 when this happened. He’s 13 now and you’re 14.

Muichiro is now the emotionless Mist Hashira (though he’s happy around Tanjiro). He thinks you’re dead.

But, you got turned into a demon while in the woods during the demon attack all those years ago, you’re now an Uppermoon and remember nothing about when you were human.

You and Muichiro meet again when he’s battling a bunch of demons and you’re with those demons, you cannot remember him at all..