Eun-gyeol gets stuck in 1995 and doesn't know how to return to the present. What's worse is that he meets his young father, Yi-chan, who can talk and wants to start a band to impress a girl who isn't Eun-gyeol's mother. Eun-gyeol poses as Yoon Dong-jin, a musical genius, in order to try to become a member of Yi-chan's band.

Eun-gyeol encounters Se-gyeong in her teens and learns a few things about her life that don't make sense in the future. Meanwhile, Yi-chan meets Chung-ah for the first time, but she doesn't say a word. Yi-chan tries to get away from Eun-gyeol, but Eun-gyeol follows him to the Snail Guesthouse and ends up becoming Yi-chan's math tutor.

Eun-gyeol resolves to stop the accident that caused Yi-chan to become deaf and clings to him, vowing to teach him everything he needs to know. He even promises to gift him the band Yi-chan needs. However, the school festival is in one month, and the person Yi-chan is doing this for has left the country and isn't going to return.

Everyone is confused at Se-gyeong's return, especially Eun-gyeol, who sternly warns her to stay away from Yi-chan. However, it doesn't work, and Se-gyeong approaches Yi-chan with different intentions. Meanwhile, Chung-ah can only stand by and watch as she realizes she's lost her chance to tell Yi-chan how she feels.

Chung-ah wakes up, realizing she's lying on a hospital bed, with the revelation that Yi-chan carried her there on his back. Later, Yi-chan learns her name from her tag for the first time. Meanwhile, Eun-gyeol has been silent for days, causing concern for Yi-chan. Attempting to locate him, Yi-chan hands out flyers and ends up facing trouble with local thugs. Se-gyeong desperately meets with each band member to verify something important.

Eun-gyeol wakes up at the house of the Jinsung Family after the accident. He finds out that Chung-ah was the daughter of Chairman Yoon Gun-hyung. Meanwhile, Yi-chan is hospitalized after getting beat up by the local thugs. Se-gyeong tells him that Chung-ah was the one who called for help to save him. Meanwhile, Eun-gyeol decides to help Chung-ah learn the sign language.

Astounded by Eun-gyeol's candid love confession for Se-gyeong, Yi-chan retaliates with a spirited punch. Eun-gyeol's attempts at self-defense lead to Yi-chan having a bleeding nose on both sides. The schoolyard transforms into a battleground as students try to intervene, and the entire situation gains momentum. Se-gyeong (actually Eun-yu) is left in shock by the unexpected confession. Meanwhile, Eun-gyeol uncovers a hidden secret about Chung-ah.

Eun-gyeol can't hide his feelings for Se-gyeong and ends up kissing her. Chung-ah's stepmother calls Eun-gyeol separately and tells him to quit before he teaches Chung-ah sign language. The members of the band decide to change their band name and theme right before the festival and ask Se-gyeong and Chung-ah for help. Meanwhile, Eun-gyeol learns that Master has sent a helper for him.

As the festival draws near, the boys are intensely focused on fine-tuning their band performance. Meanwhile, Eun-gyeol reflects on a pivotal clue related to a potential accident leading to hearing loss. Believing Dong-jin to be the helper that Master mentioned, he pleads with Yi-chan to skip the rehearsal, but his request is dismissed. Meanwhile, Eun-yu grapples with the challenge of uncovering her mother's genuine first love.

Eun-gyeol successfully cancels the rehearsal and prevents Yi-chan from getting seriously hurt. Chairman Yoon extends the contract with Eun-gyeol and changes the terms and conditions. The day of the festival is finally here, and Se-gyeong has to choose between Eun-gyeol and Yi-chan. Chung-ah decides not to show up at the festival.

As the enchanting glow of their festival fades, Eun-gyeol and Eun-yu acknowledge the depth of their feelings, hoping for a lasting connection. Meanwhile, the anticipated disbandment takes an unexpected turn, giving the boys another shot at the stage. The hurdle now is creating their own song, and Yi-chan suggests a gathering for this endeavor while musing on how to persuade Chung-ah to join.

Eun-gyeol and Se-gyeong realize that they’re both time travelers. He learns that Se-gyeong also had a mission to accomplish while she was in 1995. Eun-gyeol finds out that Chung-ah has been confined and abused for the past 12 years. Meanwhile, Se-gyeong tells Eun-gyeol that Yi-chan’s accident didn’t happen on the day before the festival and that it hasn’t happened yet.

Eun-yu drops clues about Yi-chan's real hearing loss incident to Eun-gyeol. Knowing that Eun-gyeol tends to shoulder blame for everything, she pledges to support him through this tough time. However, suspicions linger in her mind about the complexity of her connection with Eun-gyeol. Together, they methodically investigate everyone linked to the accident in search of the truth. Meanwhile, Yi-chan assures Eun-gyeol that he won't leave the house for the entire day.

Yi-chan gets hit by a car and loses his hearing. Master tells Eun-gyeol to go back to his time, but he refuses, determined to catch the guy who hit Yi-chan. Se-gyeong convinces Eun-gyeol to return to 2023, and when he finally does, a completely different life awaits him.