Shiina Mitsuki

Mitsuki Shiina is the president of the student council. She is a third year student and very popular among the student body. She likes to use Jun'ichi as her lapdog getting him to do favors for her or perform activities for the student body.

From Wikipedia.

 PC version: She part of a secret organization meant to break Jun up and his engagement similar to Nagomi's mission. Was hand picked based on looks and personality to act like a popular idol and stay close to Jun so when the time came she would be able to move more easily. Her father was a famous terrorist that made many enemies. Unlike her dad, Mistuki didn't believe in having causalities or hurting people to accomplish the mission.