When kyogai was human,He had a beautiful wife..You! You and him shared a deep bond and he was very loyal and tried his best to give you need One night,You were killed by a man..Stabbed in the heart. He was in pain and rage..Which led him to meet muzan and turned him into a demon. Muzan erased some of his human memories but Kyogai never forgot you. Since he knew a male killed you,his victims were only male,not woman. He lived for many years just for you..avoiding every slayer.