Tamayo/Relationships

Yushiro
It's unknown how these two met, but it was most likely due to Yushiro's unknown illness that was unavailingly treated by Tamayo. When he was about to die, Tamayo asked him if he either wants her to save his life by turning him into a Demon or to let him succumb into his illness. He decided to become a Demon, and since then, Tamayo took him in as her personal assistant and a medical practitioner. He also developed strong romantic feelings towards her, becoming very possessive of her, to the point of becoming angry when someone was even dwelling too close in her presence, hitting Tanjiro multiple times (which deeply annoyed her) and becoming visibly distressed seeing Tamayo being hugged by Nezuko. However, these feelings weren't reciprocated since Tamayo never got over the loss of her husband and children.

After sensing Tamayo's demise from Muzan's hands, Yushiro became deeply angered, swearing to kill Muzan by any costs.

Nezuko Kamado
Nezuko is seen to be at ease around Tamayo, acting more childish than she would normally. She sees Tamayo the same way she views all humans: a part of her family, specifically an individual similar to her mother. This endears her to Tamayo, as she is touched by the fact that Nezuko views her as a normal person, despite her status as a Demon and her past sins.

Kagaya Ubuyashiki
It's unknown how these two met or what their relationship is, but after Tanjiro's trial before the Hashira is over, Kagaya tells Tanjiro to give her his regards as Tanjiro is carried away by two kakushi towards Shinobu's house, also known as the Butterfly Mansion.

Shinobu Kocho
Upon being requested and offered by Kagaya Ubuyashiki to help the Demon Slayer Corps to kill Muzan once and for all and Tamayo accepting his offer, she was immediately introduced and set to work with Shinobu due to her own immense skills in drugs and poisons working well with the Insect Hashira's own.

Initially there was little trust between the two, with Tamayo being initially scared of trusting a Demon Slayer, especially a Hashira due to her status as a demon, and Shinobu's own paranoia and prejudice against her for being a demon. However, eventually through their work together in creating the humanization drug and anti-Kibutsuji concoction, the two developed a genuine sense of friendship and respect for each other, with Tamayo being genuinely impressed by Shinobu's talent in poisons and Shinobu being seemingly touched by the demoness's attempts to make up for her past actions and her being impressed by the latter's immense skills as a doctor.

It was also revealed that Tamayo also had a hand in personally modifying Shinobu's body in preparation for her duel and eventual death against Upper Rank 2 Doma in order to fulfill her vengeance for her older sister Kanae Kocho, showing just how much she had come to trust Tamayo to the point of allowing her to personally alter and modify her body, which could potentially damage/destroy her body.

Muzan Kibutsuji
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.