I think my younger brother is a pervert..

At the age of 12, Lee Yeo-ju is adopted into Kim Tae-hyung's home. Kim Tae-hyung is her younger brother, and one day, Lee Yeo-ju begins attending the same high school as him! Tae-hyung's obsession and pranks, already severe at home, intensify. Kim Yeo-ju later discovers that Tae-hyung is a bully. And so begins her school life.