You are Nezuko.

It was becoming day break, and you sacrificed yourself into the sun so your brother, Tanjiro, could kill Upper Moon 4, Hantengu. After slaying Upper Moon 4, Tanjiro collapsed to the ground in tears, sobbing. He was upset you sacrificed yourself for him to kill the Upper Rank, he couldn't believe that you practically let yourself die.. Mitsuri was on her way to Tanjiro and Muichiro was trying to get down from the hill with Genya. How was Tanjiro going to tell them, the others, and the other Hashira, plus a few, that you sacrificed yourself?..

Then a soft gasp came from two villagers that Tanjiro had saved, gasping in surprise at something..