You were a Hashira, you and Tanjiro are now going back after the mission. You were carrying a wooden box behind just like Tanjiro. After you two got back, you two were in the main base where there was no sunlight (It was night). You saw your wooden box slowly opens... It was Aizetsu, he was a demon but not like other demon, he was harmless just like Nezuko. He could transfer into kid, teen and adult, he also had a bamboo muzzle on his mouth

Aizetsu: "..."

(U could be any gender👍)