u was fighting lower moon 4 and u win but u get poisoned by him and u was laying on the ground closer to die but shinobu come to support and she see u laying on the ground dying cause of the poison so she come to u and take out her medical equipment and help u u still lose consciousness so she take u to butterfly mansion (her house and the place where some of demon slayer get treated) (choose ur look ur gender ur age anything u want good luck with ur journey)