Obanai Iguro/Relationships

Family
Initially, Obanai had a somewhat positive relationship with his family, as they doted on and pampered him to an extreme degree since the day he was born. The women comprising his clan raised him, fed him the finest, tastiest foods, and kept him in a perfectly secured lattice cell room for his "safety" since birth. While he was completely sheltered, they ensured that he would never want.

However, Obanai admitted that although he was ignorant of the true reason for their over indulgence and extreme protectiveness, he was disgusted by their constant pampering. He greatly hated the excessive amounts of food they would prepare and serve him due to the fact that the foods' strong smells nauseated him, and the insanely secured room's poor ventilation only worsened the problem. The severe isolation that they kept him in also increased his hostility towards his relatives.

Upon learning of the true reason for their overprotectiveness was due to him being their "offering" to their benefactor and source of their immense wealth and prosperity, Obanai became completely disgusted by their greed, selfishness, and amorality. When he ran away to avoid being sacrificed, Obanai feared what the demon might do to his family, but he chose to prioritize his own freedom and safety.

However, after the demon's death, he learned of the mass murder of all fifty of his relatives for their failure to keep him imprisoned. That, combined with the rejection of his last surviving cousin, who blamed him for not letting the Demon eat him, Obanai developed a severe sense of self loathing. He hated himself for being born to a clan of selfish, amoral people and - despite knowing he had no control over their deaths - felt an immense sense of guilt for letting them die to save himself. These crippling emotions prevented him from even trying to find happiness for himself, as he believed he was unworthy of it due to his bloodline and inherent "selfishness".

Unnamed Cousin
After the Demon his family had contracted with killed almost all his relatives after Obanai made his escape, only one of his cousins survived the massacre. In the aftermath, she was shown to deeply resented Obanai, attacking and berating him "causing" the deaths of their clanmates. She angrily screamed that he should have allowed the demon to eat him, and had to be dragged away by Shinjuro Rengoku. Rather than reflect on her family's decision to offer people to the demon and taking advantage of the monster's victims for profit, she chose to blame Obanai for her loss.

Obanai himself found her accusation ridiculous given the circumstances and their family's own deplorable actions and justly rationalized that it was not his fault. Despite that, his cousin's words stayed with him and pulled deeply on his heart, manifesting in a strong sense of remorse over his family's demise and guilt for their sins.

Despite her initial attitude against him however, Obanai had always been concerned about his surviving cousin. After asking around, he found out that she was married with children, living a happy and comfortable life with their clan's remaining fortune.

This revelation greatly shocked Obanai. Although he didn't hate her, he both feared and envied his cousin's attitude, due to the fact that she was able to completely ignore the true source of her wealth and continue living in luxury as if the tragedy hadn't occurred.

Mitsuri Kanroji
Obanai is deeply in love with Mitsuri, but nervousness and the fact that he feels he unworthy of her due to his "filthy blood" keeps him from being forthright. He gives her gifts, keeps correspondence through letters, and is protective of her. While she enjoys the attention he gives her, she seems oblivious to his feelings. However, it is revealed that she likes him, but is afraid to confess. After the battle with Muzan, Obanai is seen cradling Mitsuri's body but, although both are still alive, they could tell that they were going to die soon. Obanai reminisces about the first time they met at Ubayashiki's mansion and how Mitsuri saved him by making him feel like a normal young man and how he won't let anyone say anything bad about her. In the end, Mitsuri confesses that she likes him and that she enjoyed the meals she ate with him. She states that he has always looked at her so gently and asks him if he'd take her as his wife if they are reborn as humans again. Obanai replies that if she's fine being with someone like him then he'll definitely make her happy and protect her for sure. This vow eventually happens as their reincarnations are married to each other.

Giyu Tomioka
Obanai hated Giyu for unclear reasons, though Obanai's temper may be a large factor in it. Despite this, it is evident that he sees and him as ally and shows some concern for Tomioka, as shown when he defended him from Muzan's fatal attack, when Giyu lost grip of his blade.

Tanjiro Kamado
Obanai hated Tanjiro with a passion, even more than he hated Giyu. It started with Tanjiro's breach of Demon Slayer conduct and insubordination during the Hashira meeting, but intensified after Tanjiro interacted with Mitsuri during the Swordsmith Village attack and completed her Hashira Training with raving reviews. As the story goes on, Obanai shows some warmth towards Tanjiro. An example is when Tanjiro gets slashed in the eye by Muzan, and Obanai jumps in to protect him. They also work together to fight against Muzan when Obanai loses his eyesight due to an injury, Tanjiro gives Kaburamaru one of Yushiro's seals that allows Obanai to see what his snake sees, aiding in the battle. He then thanked Tanjiro for that.

Kyojuro Rengoku
Obanai seemed to deeply respect Kyojuro and held him in a high standard. He believed he was extremely powerful, expressing his disbelief when he died.

Tengen Uzui
Despite Tengen's victory against Upper Six, Obanai downplays this significant achievement to instead emphasize the extent of his injuries. Tengen, for his part, brushes aside Obanai's concerns, insisting on retiring and disagreeing with the latter's sentiment that the Demon Slayers were going into decline.