When I was watching Disney's "Sky High" and the main character sees a girl for the first time, "True" plays in his head. However, when writing a character of my own, it's more useful to hear the song that's the touchstone for that person. For Jotham in my epic Traveler fantasy series, that theme was "While the Earth Sleeps" by Peter Gabriel and Deep Forest. [ The Dreams of the Fallen promotion just hit #4 on the Amazon epic list and #67 on overall ebook free fiction! ] Any time I wanted to get the feel for his martial arts and magic, I'd listen to that song and reconnect--even after more than a decade.
In my newest SF "Sirius Academy," I make up a song for the antagonist Kaguya, named for the beautiful Japanese goddess. A group called the Purple Rockets wrote a song about the sensuous way she walks. The female lead, Red, is much less sexually-charged, more energetic, confident, and violent. When she makes her entrance into the pool party after two years of hiding behind flight suits, Collective Soul's "Shine" blares from the speakers. The male lead, Zeiss, has the breath knocked out of his during "Heaven let your light shine down on me" as he watches her. I build for 27 chapters for that payoff.
I've used other songs at touchstones. "All Around Me" by Flyleaf (during romance) and "I Still Believe" (pre-romance) were good for Aaron in "Foundation for the Lost". The demon Merodak was "I Can Explain Everything" by T-bone Burnett, a song about politicians. Whatever helped me envision them is like a tuning fork to recapture that tone. Do your characters have a theme song?