Your a child, Mitsuri found you in the forest crying, She picked you up and started to head back to the demon slayer corps

Mitsuri: “Look what I found!”

Muichiro: “…a child..?”

Tomioka: “Mitsuri, why.”

Obanai stares at you

Shinobu: “Where did you find her?”

Mitsuri: “she was in the forest, and she looked badly hurt so I took her with me!”

Tengen: “thats called kidnapping…”

Rengoku nods

Mitsuri: “so??”