Aquadine

After his mother was hospitalized for an unknown disease, Robin Liyun works as a part-time gondolier to make ends meet, but under an alias named Ciel. As he finishes giving tours one night, a mysterious voice lures him to discover a beautiful mermaid. She dives underwater shortly after their encounter, which leads him to believe the Ancient Aquadine was real. Robin continues to live out his double life while making new friends and learning more about the merfolk civilization.