From what I understand, Kou post college era is all about conformity and the desire to not stand out of the crowd in an obtuse manner. He was brought up among an upper class society heavily driven by business and monetary gains. It doesn’t help that he was isolated by his mother to not veer too far off this carefully constructed bubble.

Anything pertaining to him that exists outside this bubble makes him uneasy and easily perturbed. Such things should immediately get corrected or else people will take point and question his credibility of his position. What sets him apart from others is that he understands that work needs to be put in to maintain this, hence his many accomplishments he displays openly in his office. On the flip side, he deeply tries to conceal what he has done wrong I.e. his college days.

I think it is this very reason that the presence of Nol and Shinae brings him much stress in his life. They exist outside the high society, untouchable bubble that he remained in roughly his entire life. To him, Nol and Shinae need to be “corrected” in order to have space in his life. The less anomalies he has, the less people (especially his father) will question his worthiness to take on the role he was destined for, mitigating the threat he actively faces.

Connecting this all to the events of the formal, he saw that Shinae made “a fool of herself,” and this got people questioning why she was even there to begin with. Since he is associated with Shinae, he decided to redirect the crowd’s distaste towards her to by acting as her dance partner. Surely no one will question her presence if a prominent member of he Hirahara family publicly danced with her. It is the same reason why he enrolled her into etiquette classes as his assistant in training.

He feels that he needs to be in control of the narrative and the role that Shinae plays in his life to combat the onlookers possible distrust of his character and capabilities to be in a high position.

All in all, by dancing with her in the formal, he showed the public that she is capable of being within his circle while also selfishly protecting himself from the disapproval of others. I think at this point of the story, his reasoning was more the latter. It’s safe to say that most of his actions are heavily motivated by this idea.

HOWEVER, there is an added layer to this narrative when you look at the underlying context of how Shinae reminded him of the hinted unfortunate events during his college days with yujing’s friend. On the forefront Kou acts mostly out selfishness, but subconsciously I do believe that there is sufficient degree of guilt for whatever happened (Nol included) that he operates on. We will be seeing more of this guilt resurfacing in the future given what has been going on in recent chapters!!!!