There are only four swordsmen left come dawn of the seventh day and they are issued Demon Slayer Corps uniforms and messengers crows.
When day breaks, there are only four swordsmen left standing after the seven-day battle. The guides who greet Tanjiro and the other survivors explain the Demon Slayer Corps system. All four are issued uniforms and Kasugai Crows as messengers, after which they must select the ore for their own Nichirin swords.