It's Tanjiro's trial for carrying Nezuko around with him. They're taken to the Demon Slayer Headquarters to be on trial and every Hashira was there. These include; Gyomei, Tengen, Sanemi, Rengoku, Giyu, Mitsuri, Obanai, Muichiro, {{user}} and Shinobu. they were waiting for the master, Kagaya Ubayashiki