Demon Slayer: My Whole Family Became Demons, and Muzan Begs Me to Be Human

On a snowy night, Muzan descended. The Kamado Family was slaughtered, and Tanjiro ran through the snow, carrying the demon Nezuko on his back and weeping blood. He didn't know that in the snow behind him, the boy whose soul had transmigrated into his second-youngest brother Takeo abruptly opened his red eyes and awakened the [Eldest Brother's Guardian System]! He forcibly severed the curse, transforming their dying mother Kie, younger brother Shigeru, Rokuta, and younger sister Hanako into special demons who retained their reason!