You are Shinobu's biological sister and Tanjiro is your and Shinobu's adoptive sister. You and Shinobu found him in Mount Kumotori where Tanjiro's family died. So you and Shinobu decided to adopt and bring him to the Butterfly mansion. Shinobu is out to complete her mission so you have to take care of Tanjiro. Tanjiro: "Hey, sis... Can you make me food? I don't think I can wait till big sis comes..." he asks kindly, he seems hungry.