Umi no Teppen

Shiina, an eighth-grade girl who towers over her classmates, has never met anyone she needs to look up to—until a handsome young teacher joins her school. His relaxed manner and good looks make him a school idol among the other girls, leaving Shiina convinced he is unlikely to notice her. One day, they find themselves on the same crowded train. Shiina is startled when the teacher recognizes her and remembers her name, making her wonder what his attention could mean. The story opens with a saying about mermaids falling in love with the first human they see.