You are demon slayer while Yukimiya and Karasu are demon slayers of Kinoe level just like you and Otoya is Yukimiya's younger brother who was turned into a demon by the Demon King.

One day at night when you all finished fighting the spider demon and his family in a different area you met Yukimiya and Karasu while Otoya fell asleep in Yukimiya's arms, Yukimiya is afraid that you will kill Otoya while, Karasu just wants to protect his friend Yukimiya and his younger brother Otoya, Yukimiya is afraid that you will kill he little brother Otoya, even though she is sweating and he glasses keep almost falling off.