Arisu is one of the most intellectual students at Advanced Nurturing High School and is highly respected for her status.
School Chairman Sakayanagi
Arisu has a close tight-knit relationship with her father Mr Sakayanagi, who also serves as the chairman of the high school she is in. However, this connection wasn't the reason why she got into the A-Class as it was revealed that under fair circumstances, Arisu has the capability to have mastery over most of the points of assessments — which, indeed, deserves to be among the ranks of the best students of her generation.
She and Kōhei are often seen together and as representatives of Class A, they get along very well. It appears Arisu is the leader in their standing as Kōhei is shown addressing her when asking for her thoughts on the matters with other classes. Despite their partnership, it is mentioned by Honami Ichinose that the two have disagreements on how to properly run things.
It seems she doesn't mind doing things behind his back or discrediting as she had Masayoshi Hashimoto make a deal with Kakeru Ryūen after discovering Kōhei had made his own agreement. Her actions led to him being criticized for his poor judgment from the class, this shows she has no real concern for his reputation.
She appears familiar with him as when she and Kōhei were checking out the scores of each class, they saw Class C was catching up and she knew it was due to his efforts calling him persistent. They meet face to face in the courtyard where they spoke with Kakeru remarking on how it looked as if she established her rule in the school very quickly. He swore to her that he will take down all the classes including hers so that he could rule the school as she found his declaration interesting and accepted the challenge.
No direct interaction has been seen yet between the two in the anime.
In the light novel, at the end of Volume 5, they have encountered each other, as she states she knows everything about Kiyotaka and the White Room, as well as his past. According to her, she knows him very well in fact, though he doesn't seem to recall her.
In her short story, she revealed in her dream about the sports festival how he seemed faster than Manabu in the race between the two. When she woke up from her dream, she requested Masumi to watch Kiyotaka closely, as she wondered on the reason why he chose to come to this school in the first place, and his placement in D-Class no less. She noted how much has grown since the last time she saw him and states how she will continue to look forward to their next encounter, while also expressing her desire of making him hers. She also didn't seem to mind the idea of becoming his enemy in the near future.
It is later revealed in Volume 7 that Arisu had visited the White Room along with her father eight years ago and had witnessed Kiyotaka's succeeding in the training the facility put him through, however how much she knows about him is yet to be revealed.