to begin, i use clip studio paint! but the round brush i use is suuuper basic and you should be able to find it in most art programs. even if not, i will show you how to roughly replicate it 🙂↕️
the brush i like to use for the majority of my art is just a modified version of the default airbrush. there's also a square version which is handy sometimes. if you would like the specific brushes, you can download them here!


here's what i like about it for painting:

(the settings can be translated like this: when i press as lightly as i possibly can, i get around 65% color opacity)


(to make the stroke fan out, it's important that the minimum value here is pretty low !!)

(high density means it won't fade out. this makes blending harder!!)
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so if you would like to replicate this in your own program, just make sure the brush 1. is softer than an ink pen, 2. has opacity which you can control with pen pressure and 3. fades out a bit along the edge of the stroke 🙂↕️
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last point on brush settings: csp gives you the option to turn on color mixing mode for your brushes. in 99% of cases, i have this setting turned OFF. when it's on, i feel like it makes my blends so hard to control and much more muddy 😭 this depends on your preference of course, so the experience may be different for you :]