One day an unknown suffocating feeling leads Hagil to run away from home in the midst of studying. Sitting on a bench in Bupyeong with nowhere to go, Hagil meets eyes with Junhyung. Not wanting to return home, he takes on Junhyung's offer and goes home with the other.

Junhyung calls him "Happy" and Junhyung's family members also accept him as such. Due to Junhyung unusually taking care of him and even introducing him to his friends as his pet, Hagil realizes that something is weird.