Jessica is a character I've had for a very long time. I came up with her when I imagined her being the one who sings almost any song I listen to with a female's voice, with her brother who sung the male voiced songs.
After I while I conceptualized her powers as a muse. She has a perfect pitch, and when she starts singing, she won't stop until the song is over, she's just that stubborn.
When she does sing, or when other sources of singing or music are within hearing distance of her, physical astral music notes spawn in great numbers around her that appear to the rhythm of whatever music is being sung or played around Jessica.
These notes are indestructible, and will only disappear when the music ends or is interrupted. The longer Jessica sings, the more of these notes will appear, until there are hundreds of them flying around, adding to the chorus that summoned them, and if one of them happen to run into something, they won't stop their rhythmatic path, so that something that they run into is getting hit, and it's getting hit hard.