Kou Kou Kyoushi.

Hina, a student at Nikko High School, goes out one evening with her classmate Beniko. They get split up and Hina ends up in a strange meeting with a man named Ikumi in a game arcade. The next day, Ikumi turns up as the new teacher at her school. Ikumi doesn't seem to recognize Hina but the wheels of fate are slowly moving to reunite them in what is a passionate story of forbidden love.