Muzan Kibutsuji/Relationships

Tanjiro Kamado
Although, Muzan hasn't encountered Tanjirou who has been away from home one day after murdering his entire family and turning his younger sister into a demon either intentional or by mistake. After encountering him, Muzan recognized the earrings that Tanjirou was wearing causing him to recall Yoriichi who almost killed him and stirred his endless desire to kill the young Demon Slayer. After fighting against Tanjiro for the first time, he was reminded about Yoriichi.

Nezuko Kamado
Muzan tried to murder her and the entire Kamado Family after realizing their connection to the Breath of the Sun, but for some reason turned Nezuko into a demon through either a mistake or intentionally. 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 Tanjirou. But, after Nezuko, developed a resistance toward sunlight a natural weakness of demons, 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.

Yoriichi Tsugikuni
At first, Muzan has shown to be arrogant toward Yoriichi stating that he didn't have an interest in Demon Slayers who uses Breath Styles before attacking him. However, much to his surprise was able to land multiple strikes on him after his blade turned crimson red causing none of his wounds to heal, forcing Muzan to support his head to keep it from falling off, which would result in his death and escape from Yoriichi before another assault. It was at that point that he developed both a deep hatred and fear toward the Breath Style Progenitor to where he turned his older twin brother into a demon and both proceeded to murder the other Breath of the Sun users.

Despite four hundred years, his resentment and fear toward Yoriichi remained as strong as ever to even seeing his hanafuda earrings caused him to recall their initial clash and lash out against three humans. Despite Yoriichi already being died, his visage remained even in the blood that was granted to one of the Twelve Demon Moons, Upper Moon 6, Daki after Tanjirou awakened his Demon Slayer Mark, as well as stirring his despite for either the destruction of the Demon Slayer Corps or achieving immunity to the sun.

Tamayo
In their initial encounter, Muzan turned Tamayo into a demon to cure her disease without telling her about none 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.