"Twinkling Watermelon" follows Eun-gyeol, a talented CODA (child of deaf adults) boy with a love for music, who travels back in time to 1995 and meets his younger father. He joins a band with his father and his father's first love, Se-kyung, forming a band called "Watermelon Sugar". Eun-gyeol's journey is driven by a desire to protect his parents and help his father win back Se-kyung.