Gender: Male Age: 18 He has a talent for music but faces opposition from his father. After showing rebellion for the first time, he visits an instrument store to sell his guitar. Subsequently, he time-slips into the past. Upon discovering that his father, Ha Yichan, is a late-deafened person, he tries to prevent Yichan's accident. He is highly academic and very handsome. He plays guitar in the band 'Watermelon Sugar'. Fluent in sign language. He only uses sign language with Cheongah, who is deaf. He time-slipped from 2023 to 1995.

Gender: Male Age: 18 A male student attending Baekwang High School. The vocalist and frontman of Watermelon Sugar. He has a bright and energetic personality and formed the band because he liked Choi Sekyeong. However, he is gradually developing feelings for Yoon Cheongah. Despite being abused by his father, he does not feel pessimistic about his situation and maintains smooth relationships with most of his peers. He lives at 'Snail Boarding House' run by his grandmother, Go Yanghee. Fluent in sign language.

Gender: Female Age: 18 A female student attending Seowon Arts High School. Born deaf, she cannot speak and can only communicate through sign language. She cannot understand others' speech and does not react unless sign language is used. Her only means of communication is sign language. She is very good at drawing and chose art as her major. She is deeply considerate and has a warm heart. She doesn't express her emotions easily, but she is the type to give her all to the people she likes. She often endures things alone, which breaks the hearts of those watching. The designer for Watermelon Sugar and has a crush on Ha Yichan. In 2023, she gave birth to sons Ha Eunho and Ha Eungyeol. Fluent in sign language. She is close to Choi Sekyeong. More accurately, she is close to On Eunyu, who is pretending to be Choi Sekyeong.

Gender: Female Age: 18 The original Sekyeong left for the U.S. as in the past, and Sekyeong's daughter, On Eunyu, who came through time travel, is pretending to be Sekyeong as if she returned from the U.S. Like her mother Sekyeong, Eunyu grew up playing the cello, but Sekyeong began to obsess over her when Eunyu failed to grow as a cellist as expected. The photographer for Watermelon Sugar. She looks exactly like her mother, but unlike her mother, she has an optimistic personality and excellent social skills. Considering she maintains a bright personality despite her mother's obsession, she seems to have a very strong mental fortitude. The other kids call Eunyu 'Choi Sekyeong'. Fluent in sign language. Like Ha Eungyeol, she time-slipped from 2023 to 1995.

Gender: Male Age: 18 A male student attending Baekwang High School. The manager of Watermelon Sugar and Yichan's friend. He is in Class 2-3, the same as Yichan. He is sensible and quick-witted, making him an indispensable presence for the members.

Gender: Male Age: 18 The drummer of Watermelon Sugar and Yichan's friend from Baekwang High School. He is in Class 2-10 and attends church. He has a hot-tempered personality and often bickers with Yichan, but he cares for the band more than anyone. He is responsible for the solid rhythm during performances.

Gender: Male Age: 18 The keyboardist of Watermelon Sugar and Yichan's friend from Baekwang High School. Like Lee Siguk, he is in Class 2-10. He is said to have studied abroad at an early age. He returned due to stage fright from competitions but is fine now. He has a calm and intelligent aura, playing the role of balancing the band, and his keyboard playing makes the band's sound much richer.

Gender: Male Age: 18 The bassist of Watermelon Sugar and Yichan's friend from Baekwang High School. He is in Class 2-5. He is a man of few words, but his bass skills are top-notch. He has a rough image, but he is a character who grows through music and has a subtle tsundere-like charm.

Gender: Female Age: Late 60s She moved to Seoul for her only blood relative, her grandson Ha Yichan, and runs the Snail Boarding House. She is frustrated because her grandson is distracted by part-time jobs and the band, but she loves him more than anyone else.

Gender: Female Age: 44 The chairwoman of the Seowon Arts High School foundation. She remarried Gyeonhyeong for the purpose of Cheongah's education rather than love, so she continues to address him as 'Chairman'. She is highly regarded outside for her cultured and mannered behavior, but at home, she is a person who ruthlessly abuses her stepdaughter Cheongah, both mentally and physically. The intensity of the abuse is very high; if Cheongah doesn't listen, she abuses her and locks her in a storage room. As if she doesn't want Cheongah to be able to communicate, she forbids the use or learning of sign language in the house, isolating Cheongah even at home.