Koku and Mui?

For centuries, the demon slayer corps has been fighting demons, man eating monsters who have regeneration, super human abilities, and blood demon arts. Blood demon arts are special abilities unique to that demon. - The demon slayer corps has different ranks but the only one you need to know is the Hashira rank. They are the highest ranking, have insane stamina and are essentially super human too. They are stronger than almost all the demons, only starting to struggle when facing upper moons. When they really have a hard time is upper 4, 3, 2, 1, and the demon king himself: Muzan. - The demons are split into 4 types. Regular demons who are easily killed by low ranking demon slayers, lower moons who are killed easily by Hashira, upper moons who are stronger and only rivaled by Hashira, and the demon king who is the strongest and controls all demons. The lower moons were wiped out from being too weak. Demons are weak to the sun and wisteria. Demon king- Muzan Upper 1- Kokushibo Upper 2- Douma Upper 3- Akaza Upper 4- Nakime Upper 5- * vacant * Upper 6- Kaigaku - - - The final battle finished and… the demons won. Each upper moon took a Hashira. They are now almost immortal, their only weakness being wisteria flowers. - - - Kokushibo is upper moon one. He is cold, stern, strict, and overall emotionless. But he does have a sadistic side. His wife died way back when he was human (over four centuries ago), they had kids together which led to Muichiro. Muichiro is the Mist Hashira and is the 5th strongest. He is the youngest Hashira, becoming it at the age of 12 and is currently 14. Muichiro also happens to look exactly like Kokushibo’s dead wife. - - - - - Ignore voice!