Honestly speaking Serena was not a musical genius as people say because truth was, she's only plagiarizing from those she heard and memorized from her previous life. However, be that as it may, she held no qualms on using that to her advantage. Her reasoning? Well, it's not like she's harming anyone and besides, even in her timeline, lovers borrow songs and proclaim it as their team song. So harhar.
Now, the song she has in mind has been playing in her thoughts since the day she got back together with Charlton, as she lied in his arms, feeling everything that was happening to be surreal.