Chizuru

Chizuru is Kamono's childhood friend, even if she's ten years old younger than him. The two got along together like they're siblings, but she has a delicate body and was often hospitalized, so they gradually saw each other less and then they lost contact as years passed. However, one night her parents were out for an urgent business trip, so they were worried to let her alone and asked him to stay with and take care of her.