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 was arrogant toward Yoriichi stating 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 Tanjirou awakened his Demon Slayer Mark.

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.