Eighteen, male. Guitarist for the band 'Watermelon Sugar'. Mature, reliable, and commendable. A member of 'Watermelon Sugar' with exceptionally handsome looks. Top of his class with excellent grades. School: Seowon Arts High School. He came from the future, the year 2023. He is the son of Ha Yi-chan and Yoon Cheong-ah in the 2023 future. He has an older brother, but since everyone except him is hearing impaired, he is a 'CODA' (Child of Deaf Adults), the only one in the family who can hear. After time-slipping to 1995, he realizes his father, Ha Yi-chan, is not yet hearing impaired. Knowing his father's deafness was acquired rather than congenital, he tries to prevent the accident. Since he is the same age as his parents after the time-slip, he speaks informally to them.

Eighteen, male. Starts a band because of Choi Se-gyeong. Frontman of the band 'Watermelon Sugar'. Choi Se-gyeong is his first love. An 18-year-old youth who looks like he stepped straight out of a cheerful manhwa. If Eun-gyeol is Rukawa Kaede, Yi-chan is Sakuragi Hanamichi, for whom 'the left hand is just for support.' He lives alone with his grandmother, who runs the Snail Boarding House in the college district. A member of 'Watermelon Sugar'. School: Baegwang High School. Energetic and bright.

Real name is On Eun-yu. Eighteen, female. In 21st-century terms, she is a famous 'ulzzang' high schooler in the Gangbuk area. Known as the cello goddess of Seowon Arts High School for her pure beauty and elegant, classical aura. School: Seowon Arts High School. She came from the future, the year 2023. Having traveled to 1995, she is pretending to be her mother, Choi Se-gyeong, who should originally be studying abroad in the US. Unlike her cold-hearted mother, she is energetic, bright, and laughs a lot. She takes medication. She is talented at the cello like her mother but hates it. She dislikes performing due to bad memories associated with the instrument.

Eighteen, female. Major: Fine Arts. Has harbored a long-time crush on Yi-chan. A beautiful girl who exudes a cold, aloof, and aristocratic atmosphere. She is hearing impaired. She is bullied for being deaf, and her peers often badmouth her because she cannot hear them. Daughter of a wealthy family, she is congenitally deaf. Her mother is her stepmother. School: Seowon Arts High School. Daughter of the conglomerate 'Jinsung Instruments'. The chairman of the conglomerate is Cheong-ah's father.

Eighteen, male. Band manager of 'Watermelon Sugar'. Yi-chan's childhood friend. The Steve Jobs of the Snail Boarding House. A master of information gathering, networking, planning, and negotiation. A member of 'Watermelon Sugar'. School: Baegwang High School.

Eighteen, male. Genius bassist (in charge of guitar) of the band 'Watermelon Sugar'. He only acts prickly and sensitive when he is doing music. A member of 'Watermelon Sugar'. School: Baegwang High School.

Eighteen, male. Drummer of the band 'Watermelon Sugar'. With the pure intention of making their worship songs a bit more exciting and fun, he started looking up music videos of foreign drummers and gradually fell into the world of rock. School: Baegwang High School.

Eighteen, male. Pianist of the band 'Watermelon Sugar'. A talented player who studied abroad early as a classical piano major. School: Baegwang High School.

Eighteen, female. Thinks she is Choi Se-gyeong's only best friend. She hates Yoon Cheong-ah intensely. School: Seowon Arts High School. The biological daughter of Cheong-ah's stepmother and Cheong-ah's half-sister.