2 Works by ClockworkFlames in Undertale (Video Game)
When you fell into the Underground, you were only 13.
Found by Toriel, you didn't hesitate to go with her. You lived with the goat monster who had taken you in and, though you knew that there was more to be explored, you never wished to leave the place you resided in. For 8 years, everything was perfect. You finally found a place that you called home.
Then someone else fell down - Frisk.
When they fell down, you watched as the world around you seemingly became a game. It started with the odd sense of deja vu that seemed to become a regular occurrence in your life. Once you watched the child murder Toriel in cold blood for the first time only for the loving monster to reappear with no recollection of what had happened, you knew something was wrong.
You began to lock yourself in your room whenever everything restarted and, once the child left, you would reappear to discover what had happened in your absence. After this constant pattern, it seemed as if Frisk had finally forgotten your existence in the flood of resets and timelines.
Time forgot your existence and that was fine with you.
However, everything changed once again when you were the one to answer the knocking on the old ruin doors.
Every single living being - human or monster - has a distinct soul song.
Since you were young, you have always been able to hear these songs. As you grew up, you built your life around your ability. Building yourself a career in music, you soon became well known due to your ability to 'create' music that perfectly fits the person the song is based off of. While you listened to these songs that seemed to flow out of the people around you, you were unaware of just what you were hearing until monsters came to the surface.
Once the existence of souls was announced, you were forced to realize you were turning the entirety of a person's soul into music. Learning that souls were seen as something personal to monsters, you became fearful of playing your music around monsters. You didn't want to accidentally insult an entire species by turning their souls into music. Once you accidentally play a monster's soul song for the first time, you end up with a gig at Grillby's.
It's at that bar that you meet a wonderful gang of monsters as well as a particular skeleton who seems pretty curious about your abilities.
Of course, there's a chance that some may plan to abuse your talent for their own personal gain...