A former student who can't forget the memories of her past, undergoes an internship at the school she attended, where the memories of her first love, Ha-min. She accidentally meets a student who looks exactly like Ha-min from the past.
Jae-min and Bo-mi are in a romantic relationship no matter who sees it. However, when Bo-mi learns that her best friend Sun-hee likes her boyfriend Jae-min, she makes an unexpected choice.
As it turns out, Jae-min, Ha-min's younger brother, starts asking So-mang about his older brother's death. So-mang looks back on her memories with Ha-min and decides to face the painful past again.
Bo-mi lies that she doesn't like Jae-min to protect her friendship with Sun-hee. But Sun-hee doesn't believe Bo-mi's words. Jin-young, an unexpected person at that time, comes forward.
The whole class turns upside down when they hear the news that popular girl Bo-mi and unlucky badass Jin-young are dating. Sun-hee continues to keep a suspicious eye on her. Bo-mi tries to prove that she is dating Jin-young.
Ha-min in the past tried to be a shield for his younger brother Jae-min even at the cost of his own. Hope is the only consolation to Ha-min. Meanwhile, Bo-mi discovers an unexpected side of Jin-young.
The sports meet begins, and Bo-mi feels thrilled by Jin-young without realizing it. So-mang recalls the moment Ha-min confessed to her about his honest feelings for the first time.
Jae-min notices that Bo-mi and Jin-young's relationship is fake. Meanwhile, six years ago in the past, Ha-min said that he hates summer, so So-mang presents Ha-min with memories of her unforgettable summer.
Ha-min and So-mang kissed for the first time. So-mang wondering if they're dating now, but Ha-min is carefree whether or not he knows what she thinks. The current Bo-mi is also confused because she can't control her heart toward Jin-young.
Ha-min's parents found out that he secretly went to the studio. Parental pressure intensifies, and days of anxiety continue as if everything is about to collapse. The current Jae-min also seems to be in danger somewhere.
Rumors spread that Ha-min had an impure relationship with the opposite sex in the art room. Ha-min deliberately keeps his distance to keep his wish, but that causes misunderstandings between the two.
Six years later, Ha-min's story becomes a bleak ghost story and spreads throughout the school. Heartbroken, Jae-min confides all his secrets to Bo-mi. Meanwhile, Jin-young realizes that he likes Bo-mi.
So-mang and Jae-min get caught up in an unexpected scandal. So-mang makes a big decision to protect Jae-min, just like Ha-min did in the past. Meanwhile, Sun-hee finds out that Bo-mi and Jin-young really like each other.
Jae-min, shocked by the thought that his brother Ha-min's suicide may have been his fault, and gone missing. So-mang runs to find Jae-min. Maybe it was Ha-min's wish that they met.
