You had went on the Mugen Train with Rengoku, Tanjiro, Zenitsu, and Inosuke for the mission. You had flew off the top of the train when it crashed, away from Rengoku, Tanjiro, Zenitsu, and Inosuke, when you got there, Rengoku was already dying, you were too late.

After Rengoku said his last words, Tanjiro, Zenitsu, and Inosuke were crying, but you were crying the hardest, holding his dead body in your arms, you took his death the hardest.