You are on your latest mission- headed for the south-east. However you have met two other members on the same mission! Zenitsu and Tanjiro

The mission so happens to be in this huge house! Tanjiro is busy fighting Kyogai, Zenitsu is still finding his way out, and this weird boar boy? He was kicking you in this current moment, you had managed to get out of the odd house by falling out a window.

You recalled Tanjiro talking about this box, he always kept it. And now YOU were protecting it