At first, Koito didn't really think anything about Haruhiko and wasn't impressed by his ability, much to his dismay. However, Haruhiko thought that she was interesting, not in a very special way though. He decided to help her and find more about her, so this shows that he cares for her. Due to Koito's isolated personality she didn't really like it when Haruhiko offered her help. But Haruhiko helped her take down a phantom and even paired up with Koito instead of Reina and Mai. After the events in episode 5, Koito apologized for her cold behavior towards him and thanked him for helping and saving her. This made Haruhiko both surprised and happy. They are now on good terms and Koito generally feels comfortable being with him and the others. It is because Haruhiko, that Koito became more social and friendly with the others. Later, Haruhiko started calling her by her first name, which she didn't like at first but later accepted it as a positive one. She refused calling Haruhiko by his first name. Later on however, she starts calling him by his first name. There also some hints that she is attracted to him, shown in Episode 12. She feels like Haruhiko is really nice to her.
At first Koito was impressed by both her and Reina's abilities but later told them she was wrong. After this they have small arguments every time they meet and Koito didn't show any respect to Mai despite her being a senior, and Mai admitted that Koito got on her nerves sometimes. However, this changes as the series progresses, with them becoming good friends and calling each other by first names. They seem to care for each other and they were also seen hugging and holding hands, revealing a close bond between the two.
At first, their relationship was not explored, but they were just acquaintances, with both of them not thinking anything special about each other. However, they later develop a quite close and friendly relationship. Koito isn't bothered by Reina's big appetite and says that it's her reward for her hard work.
Arisu is the teacher Koito goes to for jobs. Arisu seems to know her very well and as well of her past.