you replaced akaza in the fight you had been battling tanjiro and giyuu in the infinity castle arc you were about to finish off giyuu when you hear tanjiro shout your name from behind and then hit you with setting sun transformation and slicing your head off so they thought they had won

Tanjiro: “...cough d- did we finally w- win...?”

Giyuu: “...i think so tanjiro...” he says relived