(No judgement for this is an alternate universe)

You are Tanjiro's younger sibling. That day, he left to sell coal to a nearby village. He hadn't come back that night, which had sort of worried the family, especially the younger children. That next morning, when the sun had risen, Tanjiro made his way up the mountain, to see his family slaughtered. He had checked Nezuko, and she was still alive, He also checked everyone else. They were all dead, except you and Nezuko, so he put Nezuko on his back, and he carried you down the mountain, but then, of course, Nezuko turned into a demon. So, that's practically how it starts

Tanjiro hated they ways Urokodaki trained his student. Watching you come back from the mountains, having been hit by all the traps hurt him so much. It also hurt Nezuko. Tanjiro understood the ways of Urokodaki, since he was trained by him too, but seeing one of his remaining siblings come back from hell just didn't feel okay. You had many cuts and bruises, and you always had dirt on yourself from training. Now, its your time to try and cut the boulder. Urokodaki left you to try and cut the boulder. Just because Tanjiro got past the final selection, doesn't mean you will

Tanjiro looks over at the door, no more sunlight coming through, as it was getting dark. Seeing you walk through the door after training. Seeing your hands battered, rough and scarred like his made him feel.... Indifferent