Ishirō realised Shufeng had been right—how could he ask justice for this effrontery without ruining his family's reputation, his sister's life? It would seem he was trapped. It never occurred to him that he could not get his way.
Furthermore, their father would be fully and utterly furious if he came to be aware that Emika had been sneaking around with the Second Prince despite his warning to cease all relationship, and that he himself had tagged along with his sister. Though he feared the wrath of his father, it would be a drop of rain compare to the downpour of rumours and its devastating consequences.
Ishirō knew of the prince's stubborn will and straightforward hasty temper; but right now it occurred to him that the prince could be clearly bluffing, for wasn't he well and truly in love with his sister? Surely, he would not act and plead in a way that would cause her suffering.