Im back with beautifully written kokuzan also im now realizing you can't really use the links so I'm replacing it with a short description also most of these are not done and not all of these are solely about focused on kokuzan
——————————————————————It's like looking in a mirror
By: HerenyX
A story where tanjiro teleported to a different universe/future and is found by Michikatsu and MuzanFevers and Fruition
By: Jinchuriki12
A story where after years of being in hell Muzan was reincarnated as a sickly childLittle Lord of Darkness
By: Sweet_Kiwii
(Also Muzan and kokushibo's relationship is platonic)
A story where Muzan gets turned back into a infant and has to be taken care of by the upper moonsHeaven Is Not Fit to House a Love Like You and I
By: xVaporGothx
(Also it labeled mature for it has a bit of sexual content and it's the only finished fanfic)
A story where Muzan tries to get kokushibo to appreciate his looksEat Your Young
By: xVaporGothx
A story where kokushibo begins to take care of Muichiro after the final battle (with Muzan of course)Purple Hyacinth and Cosmos
By: CrimsonCrownest
A story about Muzan who has already reincarnated starts to remember his past life and with this he decides to become a better person
ŞİMDİ OKUDUĞUN
Kokuzan (fanfics)but on different platforms
Hayran KurguRecommends of kokuzan found on ao3