In the film, Leon the Professional, is Leon the MC and Mathilda the IC?
Also, Leon seems to look out for her and teach her the ways of the assassin’s life...which seems to give him elements from the Guardian characteristics.
Since Mahtilda seems to be driving the story...this must make her the Protagonist - which is maybe why people call her the hero of the film.
But, both characters change by the end of the story. He dies. Before that, he lives contedly alone and is kind of forced to accept her into his life. Mathilda changes at the end by walking away with the plant, and is in a new school environment...which seems to be symbolic of her new life.