Two female students, Soo-kyung and Ji-hee, both have crushes on a male classmate, Sang-min. Soo-kyung is afraid that she can't express herself well, so she asks her friend Ji-hee to write an email to Sang-min. Ji-hee continues to write emails as Soo-kyung, but gradually finds that she has fallen in love with Sang-min. At this time, Ji-hee accidentally discovers her mother's safe, which contains a bunch of love letters. The most special thing is that her mother's love story is very similar to her own. Ji-hee and Soo-kyung are college students in the same school. They both have a crush on Sang-min from the drama club. Soo-kyung, who has always been more active and outgoing, asks Ji-hee to write a love letter to Sang-min. Ji-hee expresses her feelings for Sang-min without reservation, but is forced to write Soo-kyung's name. Sang-min is deeply moved after reading the love letters and gradually becomes attracted to Soo-kyung. Ji-hee feels uncomfortable and even guilty every time she meets him, but the more she tries to avoid him, the closer fate brings them. One day, while cleaning her room, Zixi accidentally discovered a mysterious box filled with memories of her mother's first love.