Eventually Mitsuru will ask you if you have joined any clubs and then she will suggest you join the student council. There you will meet two new social links Justice and Emperor. The Emperor arcana is gotten by becoming friends with the student council president. He is a jerk but you have to agree with him in order to strengthen this link. Keep showing up to the student council to increase the link. At one point you will see him interrogating some kid who is about to slug him, intervene and your link will go up.