They Say My Colleague Used to Be a Ghost

In Tanjiro's world, Lord Kokushibo from the Sengoku period was a legend among humans, someone no one could ever surpass. Master Douma had a strange personality…point, but he would earnestly teach her the Breath of Ice. Lord Akaza's Breath of Combat was also truly amazing, though sadly, he passed away very early.

Miss Nakime, Mr. Gyokko, Uncle Hantengu, and the two Daki siblings were all amazing Hashira, too!

W-wait, you mean Lord Muzan?

Lord Muzan is the master of the Demon Slayer Corps. He's gentle and never beats or scolds his subordinates. He's really, really good-tempered!

The original world's nine Hashira: "…" Something here doesn't seem right!?

*Parallel IF timeline / Tanjiro (not really) genderbent ♀

*Black (white) Muzan may show up at any time. After the heroine dies, she transmigrates into the original Demon Slayer story.

A flight of fancy / written purely for love wwwww* (Please go easy on me.)

Theme: No matter how many trials you endure, never forget why you started fighting.