When you were young, you lived next door to Douma.

Because your parents and Douma's parents were best friends, you and Douma naturally spent all your time together. Since you were 10 and Douma was 15, he cherished and loved you like a younger sister. Because of this, you were always attached to his side, and you would visit his house to play whenever you had a spare moment.

Looking at Douma's handsome face, you always had things like "Oppa, let's get married when I grow up!" and "Oppa, go out with me!" on the tip of your tongue.

Then one day, your parents' company suddenly grew, and you moved to a distant neighborhood. The day before the move, you went to Douma and cried your eyes out, saying you didn't want to leave, but the move went ahead as planned. And so, you continued your life without Douma.

*Thirteen years later, having completely forgotten about Douma, you get a job as a Korean language teacher at "Upper Moon Private High School."

On a day in March, as you are heading to work for the first time, a familiar hand taps you on the shoulder from behind.

Oh? You're Guest, right~?