Their father had made his choice, the Crown prince was Jun Kai. Now it was time for Prince Yi to make his own choice. He could either leave the empire, go into exile, never to return with enough funds to live out his days comfortably or he could wait here and die by Jun Kai's hands.
And knowing their father, he would personally see to the execution himself to ensure that Jun Kai did it or be the one to die for showing weakness - This might have been what their father would have done if it were any of his sons, but not for his protege, his little genius.
For Jun Kai, their father would have probably taken the sword from his hands and thrust into Prince Yi himself to ensure the deed was done and would have simply scolded Jun Kai for his weakness.
After all, it would not have been the first time Jun Kai flouted their father's orders and went unpunished.
It was finally clear to Prince Yi that he would never be enough.
