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 possesive 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 get over loss of her husband and children.

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

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 Pillar's own.

Initially there was little trust between the two, with Tamayo being initially scared of trusting a demon slayer, especially a Pillar 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 eventually developed a genuine sense of friendship and respect for each other, with Tamayo being genuinely impressed by Shinbou'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 Shinobou body in preparation for her duel and eventual death against Upper Moon Two,Doma in order to fulfill her vengeance for her older sister Kanae Kocho. Showing just how much she had come to trust Tamayo to allow her personally alter and modify her body and potentially damage/destroy her body.