Yoon Seeun was the only child in her family. The moment her parents passed away in a car accident, she had no one else to turn to.

That's when Shim Jayoon's grandfather - who was indebted to Seeun's late grandfather, decided to take her in.

Years passed and the two grew up together like close siblings but things starts to shift when Jayoon - Yoon, was sent to a boarding school overseas and Seeun hasn't seen her since then. 

Now that Seeun is about to enter college, Yoon finally returns to Seoul. 

That's when things gets weird.