Why does Super Sonico always wear headphones? Just as the title asks, why does Super Sonico always wear those headphones? Is there a reason behind it, or is this just the design Nitroplus came up with?
I believe this is an example of the Never Bareheaded trope in combination with the Nice Hat trope.

Never Bareheaded: A character always appears wearing a headdress of some kind, and never, ever takes it off. It doesn't have to be a hat, any kind of headgear is fine. Furthermore, it doesn't always have to be the same headgear, the point is that this character is never seen bare-headed. This gives him a certain mystique, since while it might just be that he wears the hat because he feels like it, the fact remains that we never learn what his hatless head looks like.
Nice Hat: To show that you mean business, it's important to have style. Enter: the nice hat. It may actually have utility — even conveying special powers — but more often than not it just looks cool, or even just sexy.

Considering that Super Sonic is pretty much a half-naked model for Nitroplus, the Nice Hat trope &quot;sexy&quot; part does most certainly fit this description.