
A playful rivalry turns into something more when a cocky senior dares his classmate to win the school’s top celebrity’s heart in just 21 days.

Q meets X and is challenged to beat him in 21 days—sparking rivalry and unexpected bonds.

After X’s injury, Q tends to him closely, giving them a chance to see each other differently.

As their days together grow, Q’s feelings shift, and mutual understanding slowly deepens.

At a turning point, Q and X must face whether the “21-day theory” will define their future.