Some time ago I created a simple copic marker brush in Clip Studio Paint (actually it was so long ago it was probably in Manga Studio). It was a fun little resource when linked to this set of colours of the standard copic colour set for Clip Studio Paint.
Of course, you do these things and entirely forget about them, and then several years later you delete them only to discover people still need them, so my apologies for that. Here – thanks to the archiving of the wayback machine – is the zip file for for the brush.
Uncompress the zip file and drag the .SUT file in to your installation of Clip Studio Paint, or go marker tool submenu and select “import sub tool” to import the file.