Pretty much, music is a big deal for two specific reasons. It doesn't matter what kind of music. Singing, instrumental, just any music. Even humming is included.
The reason is because music can control Darkness and it can affect Steves if the music created has enough will for it as well. The effects are a bit different between the two, but it does affect them all the same.
The Darkness is commanded through music. The better music the musician creates, the stronger hold on the Darkness they have. The Chromatics can actually have a greater chance of warding off Darkness because of this.
Say, if a Steve stumbled upon one lone Darkness that was in the wild for a while, the fading hold of the music it was being commanded by would easily be overpowered by the Steve.
If the Darkness was just ordered to attack the Steve, the Steve would then struggle overpowering the first music if they didn't have the will and the power to.
There is also a hierarchy of type of music and how well it commands the Darkness. Basic sounds like humming are at the bottom. Instrument is in the middle and singing is at the top.
Which means a few things. One, almost all the Steves know how to play one or more instruments. Two, yes, the better the singing the better the control.
How the Steves are affected is different from the Darkness. They can't be completely controlled by it, but their will can be. If whatever Musician has enough willpower and the want, they could sing and make it so any listener wouldn't have the willpower to fight or do whatever they were trying to accomplish. Or vice versa and strengthen the will of the listeners.
A keyword there is ‘the want’. They have to want to affect others for it to happen. This allows Steves to be able to sing and create music without accidentally affecting their friends. Which is good since it allows them to practice.
The Crystals strengthen the music of whoever is holding them or who has absorbed them. Orange Steve, who is part of the Orange Crystal, is even stronger compared to Canon. He stays in the Orange village because any Darkness doesn't even have a chance to attack the village. Anyone around him also ends up with the music boost. Him and Shy are the best two musicians of the village, mostly because they stay in Orange’s house and practice.
Sabre, in his world, is quite a well known Internet based musician. He doesn't deal with stages all that well but enjoys music, so he just posts his songs online. He actually lives quite far out of town, so he doesn't deal much with people and it allows him to practice without anyone seeing him. Dude has severe social anxiety.
He was actually exploring the woods around his house to practice an instrument when he heard another instrument nearby. Sabre, curious as to who the hell else is in these woods playing music, follows. We all know how it ends.
Now how does the music from the Steves affect Sabre? Long story short, it doesn't. Pretty much music is just that, music. Sure, sad songs can make him sad if he was already in a bad mood, but it doesn't affect his willpower at all.
The beginning starts off as it always does, but Sabre gets a mild glimpse when they are attacked in the temple. The Darkness appears, and immediately goes for the two. Sabre, panicked, tries to shield Scout who manages a few shaky verses before he is corrupted.
Scout goes to The Orange village, drops him off there, before he asks to be destroyed. The Village is more shooken up at the fact they just witnessed what was probably the last Red Steve die to bombard Sabre with questions.
Orange decides to help Sabre, and quickly creates the Rainbow Hub. While he is doing that, the others start their questions. Meanwhile Sabre's just stressed as all hell and frankly just wants to go back home. He does not want anything to do with what just happened and does not appreciate the questions.

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AU Collection, Stories, and Fanart
FanfictionVarious AUs I have, either explaining the AU or a story snippet of an AU. Most of it is story snippits. Some incorrect quotes are also thrown in. There is not set update schedule, so it's going to be random.