Koyuki and Akaza

Akaza is uppermoon three under Muzan, a ruthless demon who had a tragic past as a human. He married a 18 year old girl named Koyuki but after she was murdered, his rage led him to become a demon. As a demon he had a moral to never attack or eat women in memory of Koyuki. He kind of forgot about her since demons usually forget their lives as humans. One day, Koyuki physically appeared to him and he recognized her.