Prior to the beginning of the series, Irina had known Issei from their childhood and has had a crush on him since then. She does care for Issei a great deal because even when Issei was reincarnated as a Devil and had changed into a pervert, she still loved him no matter what, though she never expressed these feelings. It wasn't until Volume 10, where she tearfully talks about Issei's kindness and hard work to the children in the audience so they could encourage Issei on his match against Sairaorg, that she expresses her feelings of love for him. In Volume 9, she was incited to mate with Issei by Xenovia in order to help strengthen Heaven's forces, nearly turning into a Fallen Angel in the process after Issei accidentally landed his face on her breasts and groped them, causing her to have "impure thoughts." The next day, she was so embarrassed, that she blushes whenever she and Issei look at each other.
In Volume 14, she told Issei about Half-Angels and the preparations of a 'union' between an Angel and a human, but later became somewhat depressed about her status as an Angel is impeding her relationship because Angels are forbidden to feel desire or lewd thoughts. She believes that there are obstacles to overcome it since, she claimed, she and Issei are childhood friends. In Volume 16, it is revealed by Xenovia that, with Michael's approval, she is currently looking for a way to make love with Issei without having to turn into a Fallen Angel, much to Irina's embarrassment. In Volume 18, it is revealed that Michael has crafted a special room that is located in a different dimension that would allow her to copulate with Issei without fear of falling. It is also revealed that she was Issei's first kiss when they were children. In Volume 19, she started to become more bold in building her relationship with Issei, such as sneaking the doorknob that opens the special room in places he goes to, sneaking into his bed at night, bathing with him and calling him "darling." She becomes slightly less concerned with falling in order to be with Issei, even offering to have sex with him.
In Volume 23, after noticing that Issei was staring Mirana's chest, Irina expressed her jealousy and became even bolder, even telling him if they went to that room she'll allow him to sleep on her chest. During the match, Irina made a proposal to Issei which he accepts. Happy with his response and becoming engaged to him, Irina gain a massive power boost that she used the holy aura of Hauteclere to send Angels flying left and right. Irina wishes to have two children with Issei, one boy and one girl.
She is a very good friend of hers, going on many missions together, but she was quite disappointed when she learned that her friend had become a newly reincarnated Devil, though they have since made up due to the alliance and the truth behind Asia and Xenovia's exile. Together with Asia, they form the Church Trio because they are often seen together praying. Irina often looks up to Xenovia as a very knowledgeable person, despite most of Xenovia's knowledge being incorrect information from Kiryuu. However, Irina tends to get extremely annoyed whenever Xenovia teases her by calling her "self-proclaiming," as Irina does often declare she is an angel and Issei's childhood friend.
She is a very close friend to her and they, along with Xenovia, form the Church Trio because they are often seen praying together. She is very supportive of Asia's relationship with Issei due to her purity and Issei's dedication and love for her. She and Xenovia are protective of Asia and always look out for her.
According to Irina, Rias was the one person in the club she wasn't able to get along with the most. Due to their different upbringings in opposing factions, Irina felt that they lived in different worlds and that the two could not coexist with one another. When Rias approached Irina about her childhood with Issei, Irina initially assumed that it was due to jealousy. However, after some time, Irina realized that, despite the different backgrounds, Rias was a normal girl like her, and the two eventually became good friends. In fact, Rias has begun to address Irina without the use of an honorific, showing how close the two have become.
He is the spiritual support for her since she found out that God died. He is also her leader as she is one of 'his' Brave Saints. Irina is also very loyal to him.
Irina and Dulio has never interacted with each other but it is shown that Irina respects Dulio for his skills and position, calling him "Dulio-sama".
Irina has shown to have great respect for Gabriel being a member of the Four Great Seraphim as well as the strongest woman in Heaven.
Griselda is Irina's superior. Like Xenovia, Irina is very fearful of Griselda and calls Griselda "Boss-sama".
Touji is Irina's father who loves her a great deal.