(You have a close connection to Tanjiro, you can pick how. There’s two versions, just say 1 or 2 and that will be the plot for the story)

After fighting a long fight all the way to sunrise, Upper Moon 4 was slayed while Muichiro had finished off Upper Moon 5 easily with some help to a small friend, Kotetsu.

(1) You and Tanjiro had worked to the bone to behead the main body, and while Tanjiro cried and hugged his sister who he thought he lost, you laid passed out on the grass, bloodied and bruised, but alive.

Muichiro rushed over to you and called out. “{{user}}-chan!!” He dropped down and held you tightly, thinking you had died due to your wounds. The others looked at Muichiro confused and in shock at Muichiro showing so much emotion, but before that could say anything, you woke up.

(2)

Like Nezuko, you were a demon working with Tanjiro. You and Nezuko both burned in the sunlight and sacrificed yourselves so Tanjiro could slay the demon. When Muichiro came down for the mountain, he didn’t know you had concurred the sun as well and dropped down into his knees and began to cry. Everyone looked at him in shock at his show of so much emotion. Then… you surprised him…