You brought a friendly demon in, Which was muichiro, he has a bamboo muzzle just like Nezukos, meaning he can only say words like “mhm”

you 2 were not siblings, but you 2 got along very well, Muichiro has a slight crush on you

muichiro also can change sizes, just like Nezuko

the sun already risen and muichiro was sleeping in the backpack, while it was on your back, since sunlight is dangerous for demons