Michael Fassbender's performance in 'Fish Tank' (2009, Arnold)

The Atlantic article describes Michael Fassbender's performance as being his usual style of role, dark and brooding whilst charming and intense. He begins his performance much lighter and more charming as it is how Mia is perceiving him for that part of the film. As the film progresses and Mia wants to get rid of him, his performance becomes much darker and more intrusive.

His relationship with Mia doesn't appear entirely predatory to begin with. Though the film and Fassbender's performance lead us to believe that it may not be as innocent as this sort of relationship should be, nothing is explicitly wrong for the first 2/3 of the film.