Symphotionals...
A long time ago the lost century was common knowledge, you know. Nobody had to hide what they knew. That was during the century as it actually happened of course, not afterwards, oh no. The world government took care of that little mess a long time ago. Except…they overlooked something. It really was an accident…not even that, a smidgen of training mixed with an error in the genetic sequence. But when those blue-eyed babies began to show up…the color of the crystal waters of the earth…strange things began to happen. It's sort of difficult to explain, researchers and scientists still don't understand the majority of it, but when these children were around…well, things brightened up. Colors were sharper and smells were more potent and sweet and music, oh, the music that played when those children picked up an instrument…that's what made the magic happen. The music…it determined the mood of the entire area, whether things bloomed or withered and if the birds sang along to the notes, and well…if that was all that happened, the government might have left well enough alone and decided that they were simply gifted musicians, with the common trait of those sparkling blue eyes…but it wasn't it…they can do…something. Something secret, something…forbidden. It was what they were bred for; after all…history must be preserved.
Kay…so that dramatic little description probably didn't explain too much, so here's the literal aspect of the idea. At the end of the lost century there was a bit of a genetic mishap. There were maybe, oh let's say…one of these cyan-blue eyed babies to every ten thousand babies born. Well, news didn't spread very far back then, of course, technology hadn't been brought up to that sort of speed, but at least a few were coincidentally given music lessons. Doesn't really matter if it's singing, or an instrument…but what they choose to put in the music actually happened. Like, let's say one of them wanted to calm someone down. They would play calming music, insert their own wishes of the person to be calm, and voila, the "target" relaxes, even nodding off to sleep if there's enough power to it. It was thought to just be really pretty music until one of them came into contact with a poneglyph that was under construction. Well, I won't spoil that…but let's say the connection between the two is very, very deep. That's when things began to click. The people were given the nickname "Symphotional" because they could literally control symphonies. After a while they figured out they could even solidify the sound, even though that was pretty much an accident too (hey, when you're seven and you get to hold that bright shiny trumpet for the first time, you're gonna want to blow into it as loud as you can…it's the teacher's own fault he got thrown into a brick wall and became deaf in his left ear)
In truth, it's actually an off-shoot of Haki. A very rare form where they can direct their spirit through sound, as well as read other spirits around them. It's split up into a majority and minority of spiritual abilities: The majority of symphotionals have a chosen instrument that best amplifies their spiritual energy. For the few that do not get this chance however, they become conductors. They have spiritual energy in their own body (such as clapping, and voice), and can help to amplify those who work with them. It's a bit of a two-way street as the more symphotionals around a conductor, the more powerful the energy.
So, that's the gist of it. Symphotionals, they can hear the music of everything around them, change it to their liking and mood, use it for physical attacks, and for those who want to make one…well, you'll find out just what the poneglyphs are to them.
(This is a One Piece story but, I takes place later in the story line.)