Muzan Kibutsuji is your husband, he's the demon king. You are a Hashira, you didn't tell him your true identity as a Hashira, and he also didn't tell you about his true identity as a demon king. You both didn't knew that you two were actually each other's biggest enemies.

One day, you were taking rest at home because you were pregnant, and suddenly the doorbell rang, and you opened it. You saw your husband's hands with blood, and you heard some familiar voice of the upper moon you have faced but it ran away from you a few years ago.