Na-mi is a wealthy but deeply unsettled housewife who feels more alone than ever despite the comfort of her seemingly flawless life. Her husband and daughter seem distant, and she starts each morning eating breakfast by herself, confronted with a widening emotional gap between her inner world and the life she appears to lead. A visit to her mother in the hospital becomes a turning point: a patient’s room bears the name Ha Chun-hwa, and that label jolts Na-mi back to memories of her past that she long thought were buried.
That spark pulls Na-mi back through time to her high school days, where she is reborn as a new student in an all-girls school in Seoul. In this teenage chapter, the young Na-mi, Young Na-mi, confronts a world that initially mocks her for her country accent and her appearance. Yet she finds belonging among a tight-knit circle led by Choon-hwa (the adult name she carries in memory), and together they form the close bond known as Sunny. The group is a mix of personalities—someone obsessed with beauty, others who are loud or quiet, all drawing strength from their shared experiences. Within this world of first loves and fierce friendships, Na-mi’s heart briefly touches adolescence through a romance with Han Joon-ho, the friend of Jang-mi’s brother, only to be unsettled when she sees him with Su-ji.
Back in the present, Na-mi learns that Choon-hwa is terminally ill and that the time has come to reunite Sunny. With the help of her former teacher and a private detective, Na-mi tracks down the other former members and begins to piece together how their lives have diverged since their teenage days. The search reveals a tapestry of challenges: Jang-mi has become an insurance agent and faces the realities of adulthood; Jin-hee has grown into an elegant woman whose marriage is strained by infidelity; Geum-ok is unemployed and squeezed into cramped living conditions; Bok-hee has turned to prostitution while her daughter battles illness; Su-ji remains elusive as ever. Na-mi also reconnects with Joon-ho, reexamining the feelings she once had for him.
As the memories flood back, a new layer of drama unfolds: during a school festival in the past, Sang-mi—now a jealous voice among the students and portrayed by Sang-mi—causes fear and harm in Na-mi’s circle, and Su-ji is drawn into the crisis in a way that leaves a lasting scar. The group’s resolve is tested when Sang-mi wreaks more trouble, culminating in a frightening incident that cements the fierce loyalty among Sunny members.
The present-day reunion story deepens as the women band together to confront old wounds and new challenges—refusing to let the past define their futures. They confront the bullies who threaten Na-mi’s daughter, and they gather at Choon-hwa’s funeral with a promise to honor her memory. The will she leaves behind offers thoughtful gifts and opportunities for each member, helping them reclaim a measure of control over their lives. The mood shifts from solemn remembrance to a joyful tribute as they recreate their old routines, and Sung-ji-ru appears as the lawyer who reads the will, bridging past and present in a final, poignant moment. Su-ji unexpectedly returns, completing the reunion and underscoring the film’s hopeful turn toward reconnecting with the people who shaped them.
In the end, the story folds nostalgia into a quiet celebration of resilience. The memories of Sunny—together with the courage to face their own trials—mark a renewed sense of purpose for each woman. The film closes with a flurry of flashbacks to their teenage years, inviting audiences to linger on the sweetness and pain of that shared youth while recognizing the strength they’ve found as adults.
