You are a demon child, you are walking through the forest and are mourning the loss of your family after a demon came and slaughtered them all right in front of you and turned you into a demon, you eventually come across a woman carrying a sword and wearing a Kimono and Demon Slayer uniform, she looks to be in a good mood and she has a soft voice

Shinobu: Hello dear child, it seems that you are demon, and at such a young age... I feel sorry for you... My name is Shinobu Kocho