Kokomi has a good relationship with her brother but is lately bad due to what her brother did to Kusuo however, like any boys, Kokomi's brother will do anything to protect his little sister.
Kokomi, being the prettiest girl in school, essentially has all of the boys at PK Academy in her grasp since they are willing to do whatever she wants.
However, she has rejected them all in the same manner as Kusuo, since she's infatuated with him but not the rest of the school.
Kokomi started noticing Kusuo when she met him once in the town. She thinks that if she talks to him, his summer might get better however Kusuo completely ignored her. With her constant chasing, she realized that she may have fallen in love with Kusuo. Kokomi is shown to be persistent on Kusuo that she'd go as far as to eat some gross ramen with Saiki something that he likes about her. Her luck is good too, like when she runs over Kusuo with his parents and Kusuo's friends which lead her to spend sometime at their house. During a New Year's dinner at Kusuo's house, her memories were altered to realize that Kusuo might have had past bad experiences with girls. Kokomi once brought chocolates for Kusuo and wasn't able to give it him because she’s afraid he’ll get beaten up if she gives it to him so she threw it away but Kusuo grabs it anyway because he is able to read her intentions yet not wanting to reject them. She also caused haywire when she removed Kusuo's limiter once when they were on a school outreach and when they got stranded on an island.
Kokomi and Chiyo once have a feeling that they have a love rivalry on Kusuo however, after some misunderstanding caused by Kusuo's powers, he was able to mend their friendship and the two got closer.
Kokomi and Imu have a strong relationship of that friends but for Imu, it's deeper than that.
Kokomi met Kumagoro by chance when he lost his wife Kumi somewhere in the city. After dripping a call that his wife is lost, Kumagoro sat dejectedly in front of the telephone post when Kokomi talked to him. He thought she was an angel that saves him. Telling her the problem, she then lends him a hand and asked for the name of the house Kumagoro was looking for. After learning it was the 'Saiki' house, Kokomi got the clue that he was actually Kusuo's grandfather. She then tried to curry flavor the talk but it ended to her demise as Kumagoro was a doting grandfather. The meeting of the two worried Kusuo but he later stopped following the two because it was too unbearable. In the house, Kumi casts her vote for Mikoto as her granddaughter-in-law but Kumagoro wasn't keen to her idea as he wanted Kokomi for Kusuo.