I'm assuming this is for an AOS? If so, how you write your essay depends on your AOS because you'd have to link whatever you've learnt back to it.
For example, the theme is Cultural Differences and my AOS is Change so my topic sentence would be "Differing cultural representations of others can inevitably lead to a change in self."
If it's not an AOS then I'm not too sure, some other themes include love, betrayal, the treatment of women, deception, relationships etc etc.