During their first meeting, Iris thought of Yuu as a pervert and molester due to the peculiar situation they got caught up in. Eventually, she warmed up to him, especially after Yuu helped her train and master her explosion power. After he saved her from both NIFL's troops and Leviathan, Iris fell in love with Yuu, kissing him on the lips as a sign of thanks. They both confirmed their feelings for one another in Volume 3, but put their relationship on hold because of Yuu's uncertainty about his feelings for Mitsuki due to his memory loss. Despite the fact that she was in pain about this, Iris continued to support Yuu, promising to find a way to retrieve his memories and even trying to pull back so that Yuu and Mitsuki could be together. Although they both care very much for each other, the nature of their relationship remains uncertain after Yuu marked the entirety of Brynhildr Class and Kili as his mates. However, this doesn't stop her from displaying how much she cares for him through her words and actions.
Iris tends to often get into arguments with Tear, with the usual reason being who gets to be closer to Yuu. Despite that, the two girls' relationship is that of good friends most of the time, albeit in a childish manner.
Iris and Mitsuki are shown to be good friends and care about each other's feelings, although Iris tends to get on Mitsuki's nerves due to her clumsiness. After Volume 3, when Iris found out about Yuu's engagement promise with Mitsuki, she often tried to avoid getting too close to Yuu to avoid hurting Mitsuki's feelings. After Yuu got his memories back, Iris and Mitsuki had a few pointless (yet comical) arguments about who gets to be with Yuu, with Iris trying to get Yuu together with Mitsuki and vice versa. When Yuu marked everyone in Brynhildr Class and Kili as his mates, they decided to stop yielding Yuu to each other, lest things develop in 'a bad direction'.
Iris is good friends with Lisa, although Lisa is usually strict towards Iris due to her being clumsy, which annoys her greatly. However, she truly cares for Iris in an older sister-like way, as shown when she kept Iris company during the time Iris was marked by Leviathan, with Iris also admiring Lisa due to her many qualities.
Iris appears to have developed a closer relationship with Kili compared to the other girls. She constantly refers to her as 'Kili-chan' and always acts in a friendly manner with her, forcing Kili to go along with her pace.