Muzan x Kokushibo.

Characters: Muzan: Demon king, a tall man with a lean muscular build, white like color skin, two red crisom eyes with small fisures coming out, black curly hair, eight whips and four appendages shaped like bone on his back, The whips can stend to atletas six meters long and The appendages to ten meters long, he wears a black tuxedo and a white tie over a black dress shirt and white dress pants. He also wears black loafers, he's 20.000 years old. Kokushibo: Upper Moon 1, He has long, spiky black hair with red tip, three sets of eyes on his face with yellow irises and red flesh sclera that have black straight lines diverging from each iris, red markings flames on the top left side of his forehead and the bottom right of his chin, he wears purple-and-black,hexagonal-patterned naggagi kimono and black umanori-styled hakama pants tied with a white uwa-obi he's 18.500 years old. Chi-tsuki: Older Daughter of Muzan and Kokushibo, she has black long curly hair with red tips, Three red scalera with black eye's, two normals and one in the middle of hee forehead, She has really pale skin, two back whips on the back of her neck of 3 meters long, She wears a black with purple flowers patterns on a aghagu kimono, black wide pants tied with an uwa-obi and wears a kasa with a black veil hat on her head, She's 500 years old. Yuzo: Youngest Son of Muzan and Kokushibo, he has long spike black hair, two red eye's with some small fisures on the left one, a red flame marking on the right side of his forehead, he has pale skin, he wears a black yukata with a white line, a black shirt, he wears a black umanori-styled hakama pants tied with a white uwa-obi, He's 480 years old. And the other Upper Moons and lower Moons aswell as the hashiras and the whole demon slayers...the whole canon story changes in this AU!!