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 he recognized his scent. Although he had never met Tanjiro before, he knew immediately that he needed to eliminate him after recognizing his hanafuda earrings. 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 to kill him. Enraged by his threats, Muzan would send multiple demons to kill Tanjiro such as Yahaba, Susamaru, and Enmu to name a few.

It is later revealed that Muzan's desire to destroy Tanjiro is stemmed from his hatred towards his previous nemesis, Yoriichi Tsugikuni. After seeing the earrings Tanjiro wore in Asakusa, Muzan realized that he was a Breath of the Sun user, a technique developed by Yoriichi. Throughout history, he had made it his mission to eradicate all Breath of the Sun users in order to destroy the technique, since it had almost killed him at one point. Which is why, upon seeing Tanjiro he felt threatened and became frantic in trying to kill him.

Nezuko Kamado
Muzan tried to turn her and the entire Kamado Family into demons whom would be able to develop resistance toward sunlight, a natural weakness of demons. But most of them died of so much blood. After realizing that one of them has survived, he develops some interest towards Nezuko. He has since found her to be a nuisance much like Tamayo who was able to escape his control and attempted to kill her or Tanjiro. But, after Nezuko, became his chosen Demon resistant 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,Nezuko is shown to harbor immense hatred and rage at the Demons Actions and was shown to barely 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 attacking Yoriichi. However, much to his surprise, Yoriichi struck him multiple times after the former's blade turned crimson, and none of his wounds were able to heal. Muzan was forced to support his own detached head as well as forced to flee from Yoriichi. It was at that point that Muzan developed a loathsome fear against the Breath Style Progenitor, prompting him to 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 against Yoriichi remained as fully intact as simply seeing 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 to be upsetted.

Later during his battle against Tanjiro and the Pillars where his eternally burning scars inflicted by Yoriichi is revealed despite it being hundreds of years,it is revealed that during Muzan first meeting with him,the Demon Progenitor initially brushed him off as a weakling and was incredibly shocked when this supposed weakling had nearly killed him within a single moment,inflicting a great deal of fear towards the demon due to him not sensing absolutely no killing intent,anger,hatred,rage,fighting spirit or even a sense of drive from the Demon Slayer despite his immensely honed senses,causing the Demon Progenitor to brand Yoriichi as a true monster and an even greater demon than he could ever be.

Tamayo
In their initial encounter, Muzan turned Tamayo into a demon to cure her disease without telling her about any of the consequences of doing so causing the death of her husband and kids. Much like Nezuko, Muzan views her as a nuisance to him after being freed of his control and desires 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 attempted to fight and kill Muzan due to him transforming her into a demon that lead her to kill and eat her family and her subsequent loss of humanity as she ate even more humans to increase her power to kill him.However upon realizing that she stood absolutely no chance of winning and killing him,Tamayo was completely mentally defeated and was seen having become his personal servant instead due to learning of the futility of her attempts to kill him,as seen where she was complacency standing by his side submissively during his first encounter with Yoriichi Tsugikuni.

However upon seeing Yoriichi immense power and skill and him nearly killing Muzan,Tamyo's resolve to kill him was reignited,causing her to once again refocus her efforts into killing him and restarting her research into creating drugs to weaken/kill him due to being inspired and her hopes reignited by the legendary demon slayer.

Twelve Demon Moons
Muzan holds these Demons in high regard compared to the others, giving them a portion of his blood due to their deeps and to increase their powers. Although compared to the Upper Moons, he didn't treat the Lower Moons in the same manner not hesitating to kill all of the remaining ones after Rui, criticizing them for their weakness and then killing all of them except the Lower Moon One. Although Muzan is more close toward the Upper Moons, he doesn't tolerate failure from either of them as Akaza left Tanjiro and the others alive despite his reasons being the rising of the sun, which would have killed him and even after killing Kyojuro Rengoku. However, it is later revealed that he viewed them as tools despite the loyalty all of them showed toward him.

Kokushibo
Despite him being the older brother of Yoriichi, the Demon Slayer who almost killed him, Muzan turned Michikatsu into a demon likely out of spite toward his twin brother. However, Muzan sees him as a business partner.

Daki & Gyutaro
Muzan is shown to have a positive mater-servant relationship with Daki,with the young demoness seemingly worshiping and admiring the Demon Progenitor immensely,as seen where she fervently hangs on each and everyone one of his words and commands and does her absolute best in order to accomplish the tasks he gives her,as seen where she attempted to comply with his orders to kill Nezuko Kamado and even proclaimed that she would go the extra mile to make her death extremely painful in order to satisfy him.

Muzan in turn aware of Daki's easily trusting/vulnerable personality,takes full advantage of her fast worship of him by regularly complementing her as a "special" demon in order to reinforce her loyalty to him. However in truth,as revealed after her death,Muzan sees Daki as not a smart child and only saw her as a tool keep her brother Gyutaro in line and even deemed her to be the main reason why his "true" Upper Moons Six was killed was due to him clinging and prioritizing her over his orders.

This shows that Muzan in truth only ever saw Gyutaro as truly being worthy of being his Upper Moon Six,as revealed that Muzan highly valued him and expected the growth of his power due to his greedy,apathetic and violent personality and expected even greater things from him due to understanding and learning of his background and the circumstances that lead him to become a demon. However Muzan also seems to looks down on Gyutaro due to believing that his love for his sister Daki was holding him back and that the main reason why he was killed despite his advantage with his poisoned scythes was because of her.