Muzan Kibutsuji/Relationships

Tanjiro Kamado
Tanjiro is considered to be Muzan's main nemesis throughout the series. After murdering the Kamado family, he was personally sought out by Tanjiro in Asakusa, Tokyo when the Demon Slayer recognized his scent from the scene of the murder. Although Muzan had never met Tanjiro before, he knew immediately that he needed to eliminate him after recognizing the hanafuda earrings he wore to be the ones his would-have-been killer previously donned, as later revealed. In an attempt to flee, he created a diversion by transforming a young man into a Demon to deter Tanjiro, but not before Tanjiro professed his goal to chase Muzan to the ends of the earth in order to kill him. Enraged by his threats, Muzan would send multiple Demons to kill Tanjiro such as Yahaba, Susamaru and Enmu throughout the series.

As aforementioned, it is revealed that Muzan's desire to destroy Tanjiro stemmed from his hatred towards his previous nemesis, Yoriichi Tsugikuni, as, after recognizing the earrings Tanjiro wore in Asakusa, Muzan realized that he was a Breath of the Sun user, a wielder of the incredibly powerful technique Yoriichi had developed and that Muzan had sworn to eradicate users of after it almost killed him. This is why, upon seeing Tanjiro for the first time, the Demon Lord felt threatened and became frantic in trying to kill him.

Nezuko Kamado
At the very beginning of the story, Muzan tried to turn Nezuko and the entire Kamado Family into Demons, however all of them but Nezuko failed to survive the transformation and instead passed away. He soon found her to be a defiant nuisance much like Tamayo, able to escape his curse and become uncontrollable. But, after Nezuko became his "Chosen Demon," developing a resistance to sunlight, Muzan didn't hesitate for a moment to attack the Demon Slayer Corps alongside the remaining Upper Moon Demons in an attempt to devour Nezuko and achieve his long-sought desire to become truly invincible.

Later, as Nezuko regained all of her memories including the painful and traumatizing memories of losing her family to Muzan in his attack on her home, she is shown to harbor immense hatred and rage towards the Demon's actions and was shown to barely be able to control herself as it all came back to her.

Yoriichi Tsugikuni
When he first encountered Yoriichi, Muzan was arrogant and stated that he wasn't interested in Demon Slayers who use Breath Styles, before dismissively attacking Yoriichi as if he'd be an easy kill. However, much to his surprise, Yoriichi struck him multiple times with his crimson blade, wounding him with deep slashes that the Demon Lord was unable to regenerate. Muzan quickly fled the scene, barely still alive, and developed a loathsome fear of the Breath Style Progenitor, prompting him to later convert Yoriichi's older twin brother into a Demon and systematically murder other Breath of the Sun users.

Even 400 years later, Muzan's fear of Yoriichi remained fully intact, as simply laying eyes on Tanjiro's hanafuda earrings caused him to recall their clash. Although Yoriichi was long dead, his visage appeared in the blood memory of Daki after Tanjiro awakened his Demon Slayer Mark, causing Muzan's fear to once again grow.

Tamayo
In their initial encounter, Muzan turned Tamayo into a Demon in order to cure her disease, hiding from her the true consequences of the transformation and so causing the death of her husband and kids. Much like Nezuko, Muzan views her as a nuisance to him after she was freed of his control, and desires for her to be killed. He didn't hesitate to mock Tamayo about killing her husband and children as well as going on a rampage out of despair killing other humans in the process, placing all the blame on her without taking responsibility for any of it.

Prior to this, hundreds of years ago, Tamayo had attempted to kill Muzan. However, upon realizing that she stood absolutely no chance of winning, Tamayo's mental state was completely defeated, her resolve and determination replaced by a docile, servant-like demeanour.

However, upon witnessing Yoriichi's immense power and skill during his fight with Muzan, Tamayo's resolve to kill him was reignited, causing her to once again refocus her efforts onto defeating the Demon Lord and restart her research into creating drugs for weakening or killing him.

Twelve Demon Moons
Muzan holds these Demons in quite high regard compared to the others, giving them a larger portion of his blood to increase their powers. However, he still doesn't treat any of them as equals, as evidenced by his quick decision to kill all but one of the Lower Moons out of anger after Rui's defeat as he criticized them for their weaknesses, and his verbal abuse towards the Upper Moons after Gyutaro's death for their failure to find the Blue Spider Lily after hundreds of years. He viewed them all as expendable tools despite the immense loyalty all of them have showed towards him.

Kokushibo
Muzan turned Michikatsu into a Demon likely only out of spite toward his twin brother. However, Muzan sees him as something of a business partner.

Daki and Gyutaro
Muzan is shown to have a positive mater-servant relationship with Daki, as the young Demoness seemingly worships and admires the Demon Progenitor immensely, fervently hanging on each and every one one of his words and doing her absolute best to accomplish the tasks he gives her.

Muzan, in turn, aware of Daki's easily trusting and therefore exploitable personality, takes full advantage of her worship by regularly complementing her, saying she's a "special" Demon in order to reinforce her loyalty to him. However, in truth, as revealed after her death, Muzan sees Daki as but a tool keep her brother, Gyutaro, in line, deeming her to be the main reason why the "true" Upper Moons Six was killed.

In truth, Muzan only ever saw Gyutaro as truly being worthy of being his Upper Moon Six, as revealed when Muzan claims that he highly valued him and expected him to grow more powerful due to his greedy, apathetic and violent personality. However, Muzan also seems to looks down on Gyutaro due to him believing that his love for his sister was holding him back and that the main reason he was killed was her.

Gyokko
During the first gathering of the Upper Moons in hundreds of years, Muzan is shown to particularly dislike Gyokko due to his arrogant and somewhat insolent personality clashing with Muzan's own short tempter and narcissism, seen when he angrily ripped off Gyokko's head when the Demon attempted to appease his Lord.

Gyokko, however, despite being brutally beheaded by him, showed absolute loyalty to the Demon Progenitor, as seen when he showed no fear, pain or anger at Muzan's actions but was instead overjoyed by Muzan holding his severed head in one hand. showing a fanatical amount of loyalty to him and was slightly annoyed by Muzan blowing him off despite him obtaining vital information on the Demon Slayer Corps but in the end considered this a good point of Muzan's personality.

Later it was revealed that Muzan in fact considers Gyokko to be one of his favorite Upper Moons due to his pots,with him greatly liking to the artistic skill he puts into them and the high price he gets by selling them.

Hantengu
Hantengu is seen to be incredibly fearful towards Muzan,especially during the Demon Lord's more violent and moody episodes,as seen when he was constantly cowering in fear of him and constantly apologizing to him during the meeting of the Upper Moons after Gyutaro and Daki's deaths putting him in a bad mood. But non the less Muzan is still shown to possess a level of trust in Hantengu's abilities and powers as a demon despite his cowardly nature, as seen when he trusted him enough to accompany Gyokko in a mission after the meeting was adjured.

Later it was revealed that Hantegnu follows Muzan not out of fear of him,but due to him being genuinely loyal and grateful to the demon lord. This was due to Muzan having "saved" Hantengu from being executed by a "corrupt" Magister who did not believe Hantegnu's claims of being "innocent" of the crimes of theft and murder by transforming him into a demon and freeing him from prison before his execution date, thanks to this Hantengu believes that Muzan was the first person to "truly" see his "innocent self" and "believe" him, causing the demon to then harbor a deep sense of respect that is even present in his other radically different disposition clones.

Upon his death at the hands of Tanjiro Kamado, Muzan was absolutely delighted by Hantengu, due to him successfully reporting that a demon that can withstand sunlight has appeared, causing the demon progenitor to laugh in ecstatic delight and actually complement the Upper Moon on his work.

Muzan in turn sees Hantengu as a "ordinary person" and sees his overly cowardly/submissive personality as annoying, but tolerable.

Nakime
Nakime exact relationship with Muzan is unknown, but she herself has shown to be incredibly loyal and obedient to the demon lord out of genuine loyalty instead of fear, as seen where she would stoically follow each and every order given to her by Muzan without hesitance.

After becoming an Upper Moon and replacing Hantengu,Muzan is shown to have become genuinely impressed and appreciative of Nakime's growth in her abilities and the further development of her powers, as seen where he actually complemented her on her growth and actually thanked her for successfully completing her mission of locating each and every Demon Slayer across the country and locating Kagaya Ubuyashiki himself, a rarity due to Muzan's own view of only seeing the Upper Moons as expendable tools and the usual degrading/arrogant/condescending demeanor he usual shows when interacting with them.

She was one of Muzan's favorite upper moons, since he believes her ability to be exceptionally useful.

Akaza
He was one of Muzan's favorites since he was loyal and serious.

Doma
Muzan never really liked Doma.