Here are some settings that simulate COPIC markers in Paint Tool SAI. Enjoy!
To add this tool:
1-Right Click on the BRUSH tool.
3-Apply all of the settings shown in the screen shot.
Rename the brush to COPIC if you wish. ^^
has kindly provided me with a screen cap of an alternate translation of SAI's tool set so the settings according to his go as follows:
BELOW the 2 brush texture and shape settings,,
Blending ->Color Blending
Dilution ->Opacity Mix
Under ADVANCED, the 3 check boxes on my screenie are: