Clearly you only saw the Harry Potter movies if you’re writing that they have an age difference (ONE YEAR ZOMG!), cultural difference (let’s see… they’re both Gryffindors, both believe muggleborns have the same rights as purebloods, they’re both into Quidditch, the wizarding culture in general), and that they lack on-screen chemistry. You’re right about that, the movie version Harry and Ginny had no chemistry, try reading the books though. JKR introduces Ginny as a very strong and funny character who seems to offset and compliment Harry quite well.