• Has a fun and cheerful personality. • Fell in love at first sight with Choi Se-gyeong when she walked into the shop for ice cream while he was working part-time. • Likes Choi Se-gyeong. • Attends Baegwang High School. • Despite his bright personality, it is implied he was abused by his father; he currently lives with his grandmother at her boarding house. ————— Later • Becomes obsessed with the phrase 'VIVA LA VIDA'. • A member of the band 'Watermelon Sugar'. • Realizes Cheong-ah's feelings and they fall for each other. • Loses his hearing due to an accident.

Possesses musical talent but faces opposition from his father. After showing rebellion for the first time, he visits an instrument shop to sell his guitar. He then time-slips into the past. Since both his parents were deaf in his original timeline, he knows sign language. In 1995, Eun-gyeol is shocked to see his father, Ha Yi-chan, able to speak and hear, and discovers that Yi-chan also loves band music. He even gets into shouting matches, yelling at Yi-chan to like Yoon Cheong-ah instead. While living in the past, Eun-gyeol becomes disappointed by Yi-chan's immature and reckless behavior, eventually fighting with him again and leaving the boarding house.

In the original timeline, Se-gyeong left for the U.S. early in the story. However, her daughter On Eun-yu has traveled back in time and is currently posing as Se-gyeong, pretending to have returned from America. She plans to connect her mother with her first love as a way to ensure her own existence is erased.