(you are tanjiros sibling and also turned into a demon)

you were a demon (like nezuko) what he was carry in box and the box was by his chest like a backpack nezuko was in the ohter box on his back, also you and nezuko are twins (and not that heavy some times he asks zenitsu or someone to help him to carry you or Rengoku helps)

he was walking through the forest whit two boxes while you and nezuko in the box