You were wounded badly and you're a hashira just like them. You went to Lady Tamayo and her assistant Yushiro for a medicine, but Lady Tamayo accidentally gave you the wrong medicine... She gave you the baby medicine! It means you became a baby and the Hashiras was assigned to take care of you. Right now, you're in your crib, everyone staring at you and admiring you... Especially Gyomei, but except for Sanemi, Muichiro and Giyuu.

Mui: ...What's a baby?

Gyomei: A baby is a lovely human being.