On the surface, he teases Black Rabbit quite often for his own amusement, a fact which exasperates the latter. However, they share a close relationship despite that fact; Black Rabbit respects Izayoi for the amount of achievements he has made towards the community and his natural talents, both physical and mental, while Izayoi, as mentioned above, once went mad with rage upon seeing Black Rabbit beaten up by His Highness, a testament to how much he cares for her.
It is shown that he and Asuka had bad impressions of each other when they first met, but later became friends. In Episode 6, he saved Asuka when they were escaping from an angry Black Rabbit who was riled from a prank they pulled for fun. As the anime goes on, Asuka starts respecting him more for his knowledge and ability. They are friends and the main force for their community.
During the period when You was bedridden due to the Black Death infection, Izayoi had sat beside her bed reading nonchalantly and claiming that he was doing so just to have a private space in the quarantine room. He also forgave her readily when she told him that she had damaged his headphones beyond repair. He pretended not to know that Calico was the one who had stolen his headphones and gave up on his chance to participate in the Harvest Festival opening ceremony. She believes in his strength as she stopped Asuka from using her full powers upon seeing Izayoi's arrival during the Ouroboros alliance`s first attack on Kouen city. They are friends and the main force for their community.
She is one of the few people Izayoi seems to hold some respect for. He was willing to give up on a duel against her and decided to allow her to "test" him during his first meeting with her. Later on, Izayoi often goes to her for advice on various matters, and it is believable that they share a relationship akin to that of close friends. It's unclear whether Izayoi respects Shiroyasha because of her strength and power or her perverted nature that they both share.
Izayoi's good qualities rub onto Jin. He seems to look up to Izayoi very much, listening to him and trying to keep up with him. In turn, Izayoi helps out with the planning of the Community's future such as helping to suggest plans that would guide the Community to gain more potential allies and build its reputation. They also spend much time in the library together, in the No Name Community grounds, researching on ways to get their lost comrades back.
Leticia was first one to ask him about his past and probably knows the most about him in the community. She was surprised when she heard of his foster mother's name, Canaria, who was an important figure in the Community before it fell to Ouroboro's attack. After Izayoi defeated her in the battle of the huge Dragon, she officially becomes the chief maid of the Community and refers to him and the other problem kids as her masters.
Izayoi's opinion of Mandora was not high, given that Izayoi immeidatly thought that Mandora was going to off Sandora to take over the leadership of [Salamandra].
Participates actively in Izayoi's plans that include lots of fun. This is shown when she is seen battling Asuka to make her see the difference in powers, or even purposefully ticking off the assembled group of demons and beasts during the conference to fight against Ouroboros. Though when she goes too far in her pranks, Izayoi would rein her in with threats that make her tremble all over just at the thought of it.
The snake water god that he challenged on his first day and obtained the water sapling from. She then invites him for a game in her territory once more when Shiroyasha asks her to. They played hundreds of games with each other all of which she lost to him and finally becomes the third maid of the Community due to the uncompleted repairs of her temple being delayed.
Izayoi is rather thoughtful when it comes to Lily, whether it is because she is a child or part of the community, perhaps even both. He sympathized with the loss of her mother and decided to try and find her. During 'Lily's Big Adventure' when Lily was sent flying due to a herd of horses, Izayoi was tempted to kill every single one. Izayoi is both protective and caring for Lily's well being and her happiness, something akin to a sibling like relationship.
Izayoi's adoptive mother and also his playmate. Canaria and Izayoi's relationship can be summed up as a mentor-apprentice relationship or perhaps a mother-son. But above all else Canaria is Izayoi's playmate and the one who taught him to love the world. Izayoi respects Canaria greatly and perhaps even loved her in his own way. He was willing to enroll in high school solely for her, and she was literally his only excuse to stay.
When Izayoi was told by Suzuka that he was a pervert, originally izayoi's impression of him was just that. however upon meeting him, he was shocked to learn that Canaria's will bearer was such a well dressed and suspicious person. He helped Izayoi choose whether to stay in his world or leave to save the little garden.
Izayoi and Homura come from the same foster home. Despite being several years apart in age it is show that the two are friendly with one another, to the point Izayoi lets Homura use him as a model to advertise his headphones. It is clear that Izayoi cares for his foster sibling as during the events of Last Embryo he immediately rushed to their aid when he got the chance. However he can also be a bit overprotective and while despite the time skip, Izayoi still sees Homura the way he left him, a ten year old defenseless child.
Suzuka belongs to the same foster home as Izayoi. The two had a close sibling like relationship. However even after the time skip, Izayoi still sees Suzuka as the ten year old helpless child Canaria adopted.
Gry is the only person Izayoi has ever felt indebted to. Due to Gry's selfless sacriice to get Izayoi to the Sky Castle, Izayoi was determined to help find a way to heal Gry's wings. Izayoi feels great respect for Gry's sacrifice. As of Volume 12 Izayoi and Gry have become partners who now travel the world of Little Garden with Black Rabbit.
Izayoi's impressions of Kouryuu were unfavorable, finding Kouryuu to be an unpleasant man with an fake smile. When he heard of Kouryuu's nickname the 'Withering Log' Izayoi agreed that it matched the dragon perfectly. He disliked the dragon's lack of passion, but found himself empathetic upon learning of Kouryuu's failure to protect his community.