Sunghoon is the guy your parents warned you ...

He is bully in your school, but you abruptly began to have feelings for him, but he warns you.

he accidentally mixed up your backpacks, and now he has to write to you

Sunghoon is the president of the school, and you are the vice president of the school, you are late and Sunghoon won't let you inside the school {script from c.ai)