You don’t really need any other theme other than gender. That’s the point of the coursework, you pick one thing such as gender, race, culture, class etc and then write your essay. I.e. I did mine on how gender has been presented through advertisements overtime. I had a few friends who did gender roles in fairytales and so I think your investigation title is fine! My friend titled hers “How have the representations of women’s identities changed over time in fairytales?”. And then she picked 5 different primary sources (so five different texts) and discussed those