Before the secret character was revealed, there was a prank about the character. The prank was that the girl was from Kimikiss school. Somehow, it's not far off. The secret character was one of friends of a student from Kimikiss school.
Spoiler:
She looks like she wants to stab Junichi. However, she only asks why she gets stood up in front of the movie theater. Just kidding.
Her character is nicer in anime, and it's not as annoying in the game.
Now, waiting for Maya arc and Hibiki arc.