This is by no means perfect, and I just slapped it together because I used to hate trying to blend in Photoshop and have the thing lag up.

So if you know how to make brushes it should be pretty easy to see what I did here. You can use your own shape, I just am showing the one I used.

The number up in the left corner is how much strength I use. Obviously, all these can be adjusted. It makes a nice smoky edge. This brush needs a tablet to work to any justice.

If you give it a try lemme know what you think as far as quality vs speed.

I'll toss this in scraps later.

Edit: The shape dynamics is just a size/pen pressure standard thing.