Obanai Iguro/Relationships

Family
Initially, Obanai had a somewhat positive relationship with his family. Having since the day he was born, continuously been dotted and pampered by his family to the most extremist degree. Having raised and sheltered him in a perfectly secured lattice cell room for his "safety" since birth, feed him the finest, tastiest foods since he was little and kept him completely sheltered from everything and gave him everything he could ever need, insuring that he would never want anything since the day he was born. However, Obanai himself admitted that although he was ignorant of the true reason for their over indulgence and extreme protectiveness to him, he himself was disgusted by their constant pampering of him, having greatly hated the excessive amounts of fine foods they would prepare and serve him due to the fact that the severe smells and odors of the food made his nose ache and the insanely secured room's poor ventilation only worsened the problem. The severe isolation that they kept him in also increased his initial hostility to his relatives.

However upon learning of the true reason for their overly protectiveness towards him due to him being their "offering" to their benefactor and the true source of his families immense wealth and prosperity, Obanai became completely disgusted by his relatives greed, selfishness and amorality. So much so that he possessed little to no care or guilt at his attempts to run away despite suspecting of what the demon would do to them if he did in order to prioritize his own freedom and safety.

However upon the demon's death and learning of the mass murder of all fifty of his relatives at the demon's hand for their failure to keep him imprisoned and the sharp, resentful, selfish rejection of his last surviving cousin, who blamed him for "selfishly" not letting the Demon eat him. Obanai still developed a severe sense of self loathing due to being born to a clan of selfish, amoral people and later despite knowing he had no control over their deaths, Obanai still developed a immense sense of guilt for letting them die to save himself despite their selfishness towards him. So much so that this even prevented him from even trying to find happiness for his own due to believing that he was not worthy of it due to his bloodline and inherit "selfishness".

Unnamed Cousin
After the Demon his family had been contracted with killed almost all his relatives after Obanai made his escape, only one of his cousins survived the massacre. Due to him having gotten their entire family killed due to running away, his surviving cousin was shown to deeply resent and hate her cousin. This is seen where she had attacked and berated Obanai for "causing" the death's of their family and angrily screamed that he should have just allowed the demon eat him rather than let it kill them, completely ignoring her clan's own horrible actions of offering people to the demon and taking advantage of their victims for profit and had to be dragged away by Shinjuro Rengoku from attacking him further.

Obanai himself found her accusation ridiculous due to his circumstances and their family's own deplorable actions and justly rationalized that given his circumstances, it was not his fault. However despite that, his cousin's words still stayed with him and pulled deeply in his heart, having felt a strong amount of remorse for causing his family's demise and guilt for their clan's sins.

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

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 to completely ignore the true source of her fortune she has and being able to go on living in luxury as if the tragedy hadn't occurred.

Mitsuri Kanroji
Obanai is deeply in love with Mitsuri, but pride, nervousness and the fact that he feels he is not worthy of her due to his "filthy blood" keep him from being forthright. He gives her gifts, keeps correspondence through letters, and is protective of her, and, while she enjoys the attention he gives her, she seems oblivious to his feelings but it is revealed that she also likes him. After the battle with Muzan, Obanai is seen cradling Mitsuri's body but, although both are still alive, they already felt 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 the meals she ate with him were the best. She also states that he has always been looking 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 that, next time, he will 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 a little concern for Tomioka, as shown when he defended him from Muzan's fatal attack, when Giyu lost grip of his blade.

Tanjiro Kamado
Obanai also hated Tanjiro with a passion, even more than he hated Giyu. It started with Tanjiro's breach of the 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 something of 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.