Umi no Teppen 

"A mermaid will fall in love with the first human she sees." Shiina is your average grade 8 girl----that is, except for her height, which makes her tower over the other people in her class. She's never met anyone whom SHE had to look up to...that is, until a young male teacher begins teaching at her school. Because of his good looks and easy demeanor though, the other girls in her grade have turned him into the resident school idol, and there's little chance of him ever noticing her. That all changes one day when they end up in the same train during rush hour. She's surprised to find that he not only recognizes her---but he remembered her name! What could this mean?