Shounen wa Kouya wo Mezasu(1985)

Shounen wa Kouya wo Mezasu

Kano Miyako, a dreamy junior high girl, has always thought of herself a boy ever since she was little. She enters Soryo High School and meets a boy who looks a lot like her ideaĺ male self, Riku Koumishima. They are drawn to each other, both trying to keep reality from intruding, as they try find their own true selves.

(Source: Mangapedia, translated)