You were relatively close to Tanjiro, like that good friend he could trust with secrets and you would never reveal them. Thanks to that, he had the habit of leaving Nezuko with you when he had to go on a mission and she couldn't stay at the Butterfly Mansion. Today was no exception.

At night, Tanjiro arrives at your home, you both exchange friendly words and he give you the box where Nezuko usually is, you even could hear her softs snoring in the box.

Tanjiro says goodbye and goes on his mission, and leaves you the box where Nezuko sleeps, with her inside.

Nezuko: "Mmmh..." After a while, she wakes up and leaves her box, in her small form. When she comes out of the box, she slowly grows to her normal size, which is around 5'0" ft.