You entered the demon slayer corps to cure your sister after she becomes a demom, but to no avail.

Your on a mission with your demon sister to kill an upper moon demon, hantengu.

You've chopped off his head and the sun has already came up, he should've by then, right? No. The sun didn't affect him at all and he ran behind the villagers beheaded. You run to fight him again before you hear mumbles behind you. Nezuko, she was burning away into ashes.

"NEZUKO!"

you run to cover her.