She seems to have close relationship with Yōsuke as when school first started she cheered on his idea of the class introducing themselves.
After several days of school, they seem to have formed a bond as they are often seen together. In truth, they're just pretending to be in a relationship in order for Kei to not get bullied in school so it is unknown how they really feel about each other.
During the survival test, when Yōsuke is chosen to watch over the boys in the class, Suzune requested Kiyotaka join him on guard duty since he needed to be watched as well. While he is picked, Kei notes on him being invisible to the rest of the class, showing that she barely acknowledges his presence in their time as classmates.
Due to his real thoughts, it is unknown what he really thinks of her.
In the light novels, their relationship is similar to the one in the anime. However, she seems to form a friendship with him which evolves into a close trusting bond with him, where Kiyotaka is shown to truly trust her more so than others, even more than Suzune and in volume 6 of the light novel, it seems that she develops a crush on Kiyotaka. Her crush on him was also hinted further in the light novel, when she became jealous of Maya's confession to Kiyotaka. Kei is one of the people who refers Kiyotaka on the first-name basis. She was also the first person to celebrate his birthday, causing him to hesitate on deleting her text messages, which he usually does. He also learned of her birthday and decided to do the same for her.
In Volume 7, even though she learned from Kakeru Ryūen that Kiyotaka betrayed her by using her from the very beginning, she still refused to betray Kiyotaka, calling him her hero, as she refused to tell Kakeru Ryūen that Kiyotaka is the true mastermind of Class D. However, she was surprised to see Kiyotaka beating up Ryūen's gang, and angrily attack Ryūen for threatening her. She was shaken by his abilities but hugged him as she was relieved that he came to her aid as he mentioned his promise to protect her.
Kei and Kikyō appear to be on good terms. In episode 2, Kei went to Kikyo for points as she was out of it after blowing through her own funds and seemed desperate for points as she used their friendship as an excuse to do so but it appears Kikyō didn't go through with it.
Satsuki Shinohara is one of Kei's friends in class 1-D.
Maya Satō is one of Kei's friends in class 1-D, as they get along well.
In Volume 6 of the light novel, Kei becomes jealous of Maya's confession to Kiyotaka.
Chiaki Matsushita is one of Kei's friends in class 1-D.