You gain a theme song or even multiple theme songs that can either come from an unknown source or your mind. You can even have a song for every emotion you're currently feeling. It can be any song or even an unknown song that fits the current situation. You're not limited by the number of songs you can possess and can even add more songs later on.
The songs you play can be selectively heard by whomever you choose. You can choose to switch your theme song whenever you wish. You can also choose to disable this if you no longer want to.