Class A Edit
He and Sakayanagi 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 over 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.
Yahiko respects Katsuragi as the Class representative and seems to follow his orders without question. This was shown when he was compliant with Katsuragi's order to stop harassing Class D after he was threatened by them and to avoid consequences for their class. During the survival test, Yahiko was amazed when Katsuragi deduced the purpose of the event though Katsuragi had told him to be silent as he didn't want anyone to overhear their plan.
Class C Edit
Not much is known about their relationship, in the survival test he two are shown forming an alliance to take down the other classes. When Katsuragi tried to shake Kakeru's hand as a sign of agreement, Kakeru told him not to overstep reminding him of his failure to reach the Student Council and walked off as Katsuragi became angry with this, showing the two have a mutual dislike.
Class D Edit
Not much is known about their relationship as they haven't had any direct interaction. They caught a glimpse of each other on the school cruise but that wasn't significant as Kōhei simply ordered Kiyotaka's group not to cause trouble.
They met again in the middle of the test when Suzune wanted to check out the cave at Class A was occupying though didn't directly interact.
Unknown to Kōhei, Kiyotaka ruined Kōhei's plan with Kakeru by sabotaging in various ways, which in turned greatly ruined Kōhei's status among his classmates.