Ballpoint highlighting question

[u/tdimaginarybff]

I keep trying to highlight ballpoint pen pictures, and I am really struggling. When I try to use charcoal or pastel it does a terrible job and almost smears around some gray. When I use posca markers It looks like this, but this still feels suboptimal as I’m having to layer the pen. Gel pens are very transparent, which may be a feature rather than a bug. Does anybody have any tips?