Every season of 21 Days Theory ever, ranked from best to worst by thousands of votes from fans of the show. The best seasons of 21 Days Theory!

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

Episode 1

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

Episode 2

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

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

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.